implications of his actions, Lennie runs away. We later learn that he has gone to a designated spot he and George agreed upon, for when trouble strikes.

Meanwhile, Curley and the men find Curley's dead wife in the barn. For his part, Curley is furious. He exclaims that he will shoot Lennie in the "guts."

As Curley gets a lynch party together, Slim and George confer privately. They agree that Lennie is in desperate trouble. George suggests that Lennie could be "saved" if they just bring him in themselves. He thinks that Lennie might just get locked up.

However, Slim cautions that Curley is still furious and will do whatever he can to get at Lennie. He also voices his opinion that prison may cause Lennie great suffering. According to Slim, the authorities may not take Lennie's mental condition into consideration and may mistreat him.

George agrees. So, the main reason George kills Lennie is to spare his friend great suffering. The other reason is that there is little he can do to prevent Lennie from committing a similar crime in the future. So, to spare everyone suffering (including Lennie), George does the only compassionate thing he can do for his friend. He takes his gun and shoots Lennie in the neck.

At the end of the story, only Slim understands why George killed Lennie.

George kills Lennie by shooting him in the back of the head to save him from a more painful death at the hands of Curley, who has vowed to make him suffer for the death of his wife. George loves his friend Lennie, whom he has looked after faithfully, and he doesn't want Lennie to die horribly, especially since Lennie has unwittingly taken the life of Curley's wife in much the same way as he petted the puppy too hard or squeezed the mice to death. Lennie didn't know his own strength. When Curley's wife screamed, he didn't know how to make her stop except to do what he did, but he did not intend to kill her.

Curley, of course, is also looking for a way to achieve revenge for Lennie's crushing his hand, so he will definitely try to kill Lennie in the most cruel way possible. He says he will "gut shoot" him. George must save his friend by a mercy killing.

People believe that George killed Lennie for several reasons. Lennie accidentally killed Curley's wife in the barn earlier. When Curley's wife is killed, George knows that Curley will likely torture and kill Lennie. Lennie would not fare well in a prison setting, nor would he be able to defend himself if Curley or the other men attempted to hurt him. George knows that he has to kill Lennie in order to protect him. Additionally, when Candy's dog is sick another one of the men takes him out back and shoots him. Candy is very sad about the loss of his dog, but he tells George that what makes him the most upset is that he knows he should have shot his own dog himself. Looking back at this, George knows that he has to kill Lennie himself so that someone else does not. He feels that it is his responsibility and he would not want someone else to do it because he loves Lennie.

George kills Lennie for multiple reasons.

•       The reason most commonly offered is that he wants to save Lennie from being tortured by the pursuing lynch mob. This is probably valid, but it does not explain why he doesn’t help Lennie escape. Lennie is hiding on the bank of a shallow river. They could wade across and climb into the Gabilan Mountains. The lynch mob might never even think of looking for them up there. Even if the mob finally guessed they had fled into the mountains, George and Lennie would have too much of a head start, and it would soon be getting dark. According to Lennie, the mountains have many caves. A mob would have to search each cave, and in the meantime the fugitives could be getting farther away.
•         George didn’t intend to help Lennie escape. This is proved conclusively by the fact that he stole Carlson’s Luger from under his bunk at the ranch. He intended to kill Lennie as painlessly as possible. When he saw the body of Curley’s wife in the barn, he assumed, like all the other men, that Lennie had tried to rape her and had unintentionally killed her while they were struggling. George realizes that Lennie is becoming a menace to society and that he would probably kill other girls if allowed to live in freedom.
•         This is the first time Lennie has killed a human being (although he has killed lots of animals). George is in some danger of being charged as an accessory to second-degree homicide. He told Lennie where to hide if he got into trouble. If he tried to help his friend escape, he would definitely be an accessory to murder.
•         George feels guilty for the death of Curley’s wife. In fact, he really is guilty because he brought Lennie to that ranch and the girl would still be alive if he hadn’t brought Lennie there. He is Lennie’s caretaker. He is responsible for any kind of trouble Lennie gets into—and he is beginning to realize that Lennie is growing into more of a problem than he is competent to handle.
•         George wants to rid himself of a big burden. He can’t handle the stress anymore. When he kills Lennie with the Luger he has mixed feelings, which include pity, sorrow, and remorse, but also a vast relief. He frequently abuses Lennie verbally, telling the childish giant that he could enjoy a much happier life if only he were free of him. Lennie is a burden because he is always getting into trouble and also because he has to be watched all the time. Lennie has caused George to lose jobs, and jobs are hard to come by. Lennie almost got both of them lynched by assaulting a girl in Weed.
•         George is angry at Lennie. He feels sorry for Curley’s dead wife. She was just a dumb girl. She should have had a chance to live out her whole life and not have it snuffed out the way Lennie had killed his puppy and so many other small animals. George kills Lennie for the same reason that the lynch mob wants to kill him. George is really fed up with his companion.
•         George can’t turn Lennie over to the authorities with the hope that they would put him in an asylum. He doesn’t have the power to determine Lennie’s fate. If he could manage to get Lennie arrested rather than lynched, the authorities would be likely to charge Lennie with murder. There would be plenty of evidence that he had killed Curley’s wife, and there would be plenty of witnesses to testify that he was guilty. The motive would be attempted rape. Nobody saw what happened in the barn. Lennie would be incapable of defending himself, and he wouldn’t have much of a defense anyway. He wouldn’t let go of the girl, she started screaming and struggling, and he killed her.
•         Lennie is showing many signs of rebelling against George’s control. He lies to George, threatens to run away and live by himself, doesn’t follow George’s instructions, sometimes deliberately disobeys. (For example, George told him to have nothing to do with Curley’s wife.) George may be a little bit afraid of Lennie, and with good reason. A time might come when Lennie might “accidentally” kill his keeper.

Steinbeck was a realist. His characters are not all good or all bad. George shows his good side by looking after Lennie for a long time. He shows his darker side by verbally abusing Lennie, by wanting to be rid of him, and finally by executing him. Lennie himself seems like a gentle, likeable character—except that he kills everything he touches, including his little puppy. Lennie is developing an interest in sex, and because of his feeble mind and giant strength he is potentially a monster who needs to be destroyed.  Slim is probably the most faultless character in the story, but he is a member of the lynch mob. He wouldn’t be present at the ending if he hadn’t come along with the mob. And there is no indication that he had any intention of giving Lennie any kind of help.

I would like to add one more thought to my answer to the question, "Why did George kill Lennie?"

We might say that it was John Steinbeck who killed Lennie. The author wanted to write a story about the hard lives of itinerant farm workers in California. At the same time, he definitely intended to adapt his story into a stage play to be produced in New York. The play could only run for a couple of hours at most, with an intermission in between. Steinbeck must have figured that he had to cut his story short somehow, and Of Mice and Men is so short that the book seems flimsy and it is called a novelette. It hardly does justice to the theme of homeless drifters struggling to survive by traveling all over California and working like slaves in the vast fields. The author's way of cutting his story short was to have one of the principal characters kill the other one. Then, of course, Steinbeck had to invent a good reason for this. He also had to foreshadow the abrupt ending and make it seem like the point of the story. Probably the only reason he had two principal characters in the first place was because in a stage play most information is conveyed through dialogue. So he needed two men who would talk to each other. If Of Mice and Men had been more of a conventional novel, there might have been only one principal or viewpoint character, as in Huckleberry Finn, Great Expectations, The Catcher in the Rye, and many other novels.

The book was published in 1937 and the New York play was produced in the same year, proving that Steinbeck was thinking about the play while he was writing the novella or novelette. Except for the scenes by the river, everything in the book takes place in two very simple settings: a bunkhouse and a barn. This is another sign that Steinbeck wanted to make it easy to adapt his book to a stage play. The scenes by the river could be simulated with nothing more than a fake campfire lighted by a couple of colored globes. The stage play was evidently a low-budget production because the subject matter was experimental for New York and no one could tell whether it would be successful.

Both the book and the play were very successful. They made Steinbeck famous. What made them successful was that Steinbeck had a genius for writing dialogue. Good dialogue conveys information and also characterizes the speaker. The dialogue spoken by Crooks, Candy, Lennie, and Curley's wife demonstrates Steinbeck's special ability. Furthermore, he understood his subject, he was sincere, he really cared about people and was really concerned about their pain.

There are really many reasons why George kills Lennie. It is often explained that this is a "mercy killing." George supposedly wants to save Lennie from the lynch mob, who will make his death as painful as possible, whereas George knows how to kill him instantly and painlessly with Carlson's Luger because Carlson has demonstrated how to do this with Candy's dog. But this explanation is an oversimplification. George has realized that Lennie is becoming a menace to society. Twice the mentally retarded giant has been involved in what could be interpreted as rape attempts, once in Weed and once with Curley's wife in the barn. George can't be watching Lennie all the time, and Lennie gets into trouble when he isn't being watched. Then he lies about it.

George realizes that Lennie is morphing into a monster who attacks young girls and is capable of killing them if they struggle. But George is getting fed up with being a caretaker, as he states repeatedly throughout the book. Furthermore, George feels responsible for the death of Curley's wife. If George hadn't protected Lennie in Weed, Lennie would never have encountered Curley's wife. George is not only morally responsible, but he believes he could be considered an accessory after the fact to that girl's murder. He is also afraid the lynch mob might turn on him because he and Lennie are so closely associated. Just before the mob leaves the ranch to hunt for Lennie, 

...Curley called, "You George! You stick with us so we don't think you had nothin' to do with this."

Curley suspects that George knows where Lennie went to hide. That in itself could make George appear guilty as an accessory. If someone commits a murder and you tell him where to go and hide and you say you don't know where he is hiding--then that makes you appear partly responsible for the murder. In the first chapter George instructed Lennie about where to come and hide if he got into trouble. That indicates that George expected Lennie to commit some serious offense, which could be interpreted to make George an accessory before and after the fact. How would anyone know that George had told Lennie where to hide if he got into trouble? Lennie would probably tell them.

George would have gotten killed by the mob in Weed, too, if they had been able to catch him and Lennie--or him alone. George is kind enough to make some sacrifices for Lennie and Aunt Clara, but he is not idealistic enough to become a martyr. George is very angry at Lennie and fears for his own life. He wants to distance himself from this trouble-maker. He cares enough to want to execute Lennie by himself, but he believes, as do all the men in the lynch mob, that Lennie must die. If he left Lennie to the lynch mob, they would kill him in a horrible manner. If he could manage to help Lennie to escape and then turned him over to the law, Lennie would get convicted of murder and executed by hanging (which was the legal method of execution in California at the time). Lennie is really only guilty of accidental manslaughter, but he would be totally incapable of explaining that to anyone. If George helped Lennie escape and didn't turn him over to the law, he could expect repetitions of what happened with the girl in Weed and with Curley's wife in the barn.

The fact that George steals Carlson's Luger in the bunkhouse shows that he has made up his mind to kill Lennie by that point. What prompted his decision was the sight of the dead girl in the barn.

Curley's wife lay with a half-covering of yellow hay. And the meanness and the plannings and the discontent and the ache for attention were all gone from her face. She was very pretty and simple, and her face was sweet and young. Now her rouged cheeks and her reddened lips made her seem alive and sleeping very lightly. The curls, tiny little sausages, were spread on the hay behind her head, and her lips were parted.

In the novella Of Mice and Men, John Steinbeck (1902-1968) uses the literary technique of foreshadowing, with respect to the character of Lennie, who, not knowing his own strength, harms or kills the items or people that were objects of his affection.  Curley's wife is killed by Lennie when he attempts to quiet her -- and Curley vows revenge on Lennie, promising he will die horribly by being "gut-shot."  

George, although he loves his friend Lennie, shoots him in the back of the head as a mercy killing to avoid being brutally murdered by Curley.

George kills Lennie because he feels responsible for Lennie's actions. As Lennie's caretaker, he was not there when Lennie accidentally killed Curley's wife. George now feels that he has to shoot Lennie as a way of showing some responsibility for what Lennie has done.

Also, Curley has vowed to make Lennie suffer and George cannot bear to see this happen. The only solution is to kill Lennie before Curley finds him. Curley is cruel. He will make Lennie's final death one of agony. George knows this about Curley. He shoots Lennie out of compassion. He is saving Lennie from brutal treatment.

George figures that Curley will hang Lennie. He knows this is a terrible way to die. He would rather shoot Lennie and get him out of his chance at a gruesome death.

Should Curley not kill Lennie, Lennie would have to be locked away for the rest of his life. George realizes this would be tremendous suffering for Lennie. He shoots him to end his possibility of being locked away for life:

When George hears the men closing in on them, he tells Lennie to look across the river. As he describes for the last time the farm that he and Lennie have so long dreamed of, he lifts Carlson’s gun from his side pocket. With great difficulty he points it at the back of Lennie’s head, and as his hand shakes violently, George pulls the trigger.

On the surface, George take cares of Lennie because he promised Lennie's Aunt Clara he would do so, but there are deeper reasons for his actions. Lennie helps George as much as George helps Lennie.

As George says early on in the story, he and Lennie have what most migrant workers don't, which is companionship. They have each other for friendship and to lean on in adversity, which makes facing their hard lives easier.

Although George often gets angry at Lennie and complains at having to take care of him, in reality, the two men have a strong, caring bond, and George loves Lennie dearly as a friend. Each complements the other: George is the type of person who likes to be in charge, and because Lennie is mentally handicapped, there is no quarrel about George making all the decisions for them. Lennie, in turn, needs George's guidance if he is to survive at all. Additionally, while George is small and wiry, Lennie is big and strong, offering George a measure of protection.

Lennie gives George's life meaning and purpose. Lennie is a friend he can confide in and a person who he knows needs him. Lennie also makes it possible for George to dream about a better future in which they can buy a small farm together. Such a dream becomes bitter without someone to share it with. When George kills Lennie out of mercy, he loses everything important to him.

George once made a solemn promise to Lennie's Aunt Clara that he would take care of him. A man of his word, George endeavors to do precisely that. Which is just as well, because Lennie is unable to care of himself. He needs George to be with him at every stage on life's journey. Otherwise, he'd likely get into serious trouble.

That's not to say that Lennie can't get into trouble even with George around. We only need to remember what happened back in Weed to see that there are limits as to how much George can protect Lennie. Even so, if George weren't there to look out for him, Lennie would almost certainly end up either killed or in prison.

It's because George wants to spare him of this terrible fate that he shoots Lennie before he can fall into the hands of a local posse after he accidentally kills Curley's wife. On the face of it, it may seem that George, by killing his friend, is going back on the promise he made to Lennie's Aunt Clara. But in actual fact, he's making good on that promise, albeit in an unusual way.

George knows that if Lennie is apprehended, then he simply won't be able to handle being incarcerated, and there'll be absolutely nothing that he, George, can do about it. And so, in order to protect Lennie and to fulfill his promise to Aunt Clara, George spares Lennie of enduring any further cruelty.

I would argue that the primary reason that George takes care of Lennie is a sense of familial obligation. George explains to Slim that he had known Lennie’s Aunt Clara, who had taken Lennie in as a baby and raised him. In the aftermath of Aunt Clara’s death, Lennie went “out workin’” with George, and the two had been together ever since. There is no doubt an element of sympathy is the reason why George takes care of Lennie, as well as an element of obligation to Aunt Clara’s memory.

Another reason why George continues to look after Lennie is the deep brother-like bond that has formed between the two of them. George is very protective of Lennie, which is why he reminds him of the mistakes that he made in the past in the hope that he does not repeat these mistakes at the new ranch.

George explains to Slim that he had once told Lennie to jump into the Sacramento River, and Lennie had done it without hesitation despite not being able to swim. This made George realize just how vulnerable Lennie was and how much he needed ongoing assistance. In a nutshell, George takes care of Lennie because he realizes that someone needs to do it and, over time, he has become fond of Lennie, despite the difficulties that he causes.

George takes care of Lennie because he has promised Lennie's Aunt Clara that he will look after him and protect him. This promise and George's moral astuteness bonds the men together. Lennie would not be able to survive outside of an institution if George were not there to ensure his safety. George views his responsibility as a burden at times, but in certain moments throughout the book one may see his true affection for Lennie, particularly through their mutual vision of a farm of their own. This sadly unattainable dream allows them to live outside of the stark reality of their lives. George views Lennie as a brother, friend, and partner in crime. Without Lennie, George would be lonely. It seems as though they need each other equally, although upon first look it seems like Lennie mostly needs George. This makes the ending of the story all the more tragic.

George promises Lennie's Aunt Clara that he will take care of Lennie, and it starts out as an obligation.  However, somewhere along the line, George's relationship with Lennie escalates to a level something similar to that of a parent protecting a child.  George sees Lennie as a child-like figure in need of protection and help, and he leads his life in a determination to give Lennie that care and protection against the cruelties of the world.

George promises Lenny's Aunt Clara when she dies that he will look after Lenny and he very loyally does just that. Some of George's reasoning is behind his promise and obligation, but as the men grow closer to one another, it becomes a deep friendship, like brothers, that only the two understand. George is very protective of Lenny and hopes that someday they can have a ranch of their own where Lenny can tend rabbits and stay out of trouble.

George stays with Lennie because he values his friendship and takes care of Lennie. It may seem that Lennie needs George more than George needs him, but in actuality, they both need each other equally. George made a promise to Lennie's Aunt Clara, who raised Lennie, that he will stay by Lennie's side and take care of him, and true to his word, he becomes Lennie's guardian.

At first, George feels obligated to protect Lennie to honor his promise to Aunt Clara. He also knows that Lennie basically cannot survive without him, due to his naivety and innocence, as well his intellectual disability. He understands that he needs to be there for Lennie, because Lennie doesn't have anyone else besides George to take care of him. As time passes, however, George begins to see Lennie not as someone he's forced to spend time with and look after but as a good friend and companion that he likes and feels very protective of.

Some argue that George behaves like a parent at times, but the more accurate description would be that George behaves like an older brother; he appreciates Lennie and tries to keep him safe and makes sure that they both stay out of trouble. In the end, George's morality and his sense of responsibility, and his love for Lennie, is what drives him to do what he believes is the right thing. He kills Lennie out of a sense of mercy, before Curley and his men come after him, to save his friend from a more painful death.

Lennie's Aunt Clara and George knew each other; after she died, Lennie started traveling around with George. George also likes having Lennie around.

When he's asked why he stays with Lennie, George says he stays with Lennie because it's nicer to travel around with someone you know. Slim finds it strange that he does so, saying that other guys don't travel around together.

George explains that both he and Lennie were born in Auburn. Clara adopted Lennie when he was a baby. Once she died, Lennie started traveling with George. Though it's not said directly that Clara asked George to take care of Lennie, it's somewhat implied.

Later on, George reminds Lennie not to run so fast because his Aunt Clara wouldn't have liked it. Lennie also remembers his aunt and says that she gave him a piece of velvet to pet. He also hallucinates a vision of her later in the story.

George stays with Lennie because he promised Lennie's Aunt Clara that he would take care of him. George also enjoys Lennie's friendship and company as they travel from ranch to ranch, searching for work as migrant farmers. In a conversation with Slim, George briefly discusses his relationship with Lennie. George says,

"We kinda look after each other...It's a lot nicer to go around with a guy you know" (Steinbeck, 17).

Despite the fact that Lennie is mentally handicapped and somewhat of a burden on George, George enjoys Lennie's company and values his friendship. In the rough, unforgiving environment of America during the Depression, many migrant farmers travel across the country by themselves. As isolated individuals with no permanent home or family, they live tragic lives and become callous, insensitive individuals. Steinbeck juxtaposes the lonely, isolated workers to George and Lennie, who have a meaningful relationship, in order to illustrate the value of friendship and brotherhood. George also understands Lennie and is used to being around him after so many years. Essentially, the two men morally support one another during the difficult time in America's history. 

George explains to Slim in Chapter 3 that he and Lennie were born in the same town and after Lennie's Aunt Clara died, Lennie just started to accompany him "out workin'." George adds that he and Lennie became used to each other so that it felt odd to be alone.

As further explanation to Slim, George tells Slim that he has witnessed many men who travel alone that have become anti-social and even mean because they are alienated and on the defensive:

"I seen the guys that go around on the ranches alone....They don't have no fun. After a long time they get mean. They get wantin' to fight all the time."

Slim agrees that the men are mean, and adds that these men withdraw and do not even talk to others.

This scene is a significant one as it underpins the theme of the fraternity of man that Steinbeck stresses in his novella set in the Depression. Steinbeck felt that in a fraternity men were stronger and could overcome oppressive conditions with the strength of others.   

In chapter 3, George is talking to Slim about how he and Lennie met. George explains that they were born in the same town. George knew Lennie's Aunt Clara, who raised Lennie from the time he was a baby. George takes up for Lennie and explains that he's not dumb, just simple. George explains that when Lennie's Aunt died, George began to take care of Lennie. He says he has never thought of leaving Lennie because Lennie is such a loyal friend.

Lennie is dependent on George because George is the only person who enables him to survive without being institutionalized. George gets Lennie jobs. The jobs provide Lennie with food to eat and a bunk to sleep in. Furthermore, the jobs pay some cash wages. Steinbeck does not show how Lennie spends his money, but he does have money to spend on necessities like shoes and on little luxuries like candy and ice cream. Without George, Lennie would not be able to get a job. He would immediately become destitute and most likely would be committed to some kind of mental asylum. The main such institution in California in those days was in Napa. Mentally retarded men were not cruelly treated there. A man like Lennie who could do hard outdoor work would be assigned to work at nearby farms and vineyards. Napa is in the heart of the California wine country, and there is always a need for labor. That is, if Lennie would conform to the rules and not try to run away. If he did run away, he would probably end up back in Napa and kept locked up. But Lennie might be satisfied with institutional life which provided a bed, clothing, hot meals, and some companionship with others like himself.

Lennie is dependent on George due to his mental state of being very child-like. He copies George numerous times throughout the play, such as the manner in which George is speaking, sitting, standing, etc. He looks up to George and sees George as not just a friend, but a protector, and someone he can emulate. Moreover, Lennie is protective of George as well (see the scene with Crooks in his room, where Crooks surmises that George is dead and not coming back). Lennie, raised by his Aunt Clara until her death, is unable to fend for himself, as George suggests when Lennie says he will live in a cave by himself. Therefore, he needs someone like George to ensure he is safe and does not do any "bad things" unintentionally (such as the incident in Weed with the girl in the red dress). Lennie does not know his own strength and is capable of doing much harm if left unchecked and unsupervised - as seen with the puppy and Curley's wife. Without George, Lennie would probably have ended up in an insane asylum or jail and eventually died. Lennie needs George in order to survive in the harsh reality that is America during the Dust Bowl. He would never be able to obtain a job or find a living situation without George to speak for him and keep him out of trouble. George is Lennie's only option of survival in life.

Lennie is dependent on George because he is mentally challenged.

Lennie is a big, strong man, but he is not mentally strong.  He relies on the smaller, quicker George.  Georgie looks after him and takes care of him.  If it weren’t for George, Lennie would be locked up or dead.  He does not know not to drink scummy water, and he gets in trouble for attacking a woman because he wants to pet her dress since it’s soft.

When George introduces himself to the ranch boss, he explains why he looks after Lennie.

“… I knowed his Aunt Clara.  She took him when he was a baby and raised him up. When his Aunt Clara died, Lennie just come along with me out workin'. Got kinda used to each other after a little while." (Ch. 3)

George explains that Lennie is not crazy, but he is “dumb as hell.”  He has the mind of a child.  He goes after he wants, knows nothing of consequences, and always has to be told what to do.  He respects and loves George.  George guides him and looks out for him, and keeps him in a job.  If he wasn’t going around with George, he could never be employed.  No employer would take the risk.  George vouches for him and takes the risk so the employer does not have to.  When something bad happens, they leave.  This is what happened in Weed, when Lennie tried to touch the lady’s dress.  They left.

In the end, even George can’t protect Lennie.  He can’t be with him all of the time.  Curly’s wife is so lonely that she goes up to Lennie, and Lennie strokes her hair.  He accidentally kills her.  Lennie did not mean it, but George realizes that the only way to really protect Lennie is to kill him.

"Yeah," said George. "I'll come. But listen, Curley. The poor bastard's nuts. Don't shoot 'im. He di'n't know what he was doin'." (Ch. 5)

George knows that if the men caught him, they would do far worse.  He also knows that if the law caught up to him, Lennie would not understand what was happening to him.  He tries to protect Lennie in the only way he can.

George stays with Lennie, because they are friends.  This might sound like a simplistic answer, but it is actually profound in the world of Of Mice and Men. In this world, there are very few friendships.  Alienation reigns supreme. All the men on the ranch are alone.  Even the men who have been on the ranch for a long time are alone. Candy is alone; he only has his dog. Crooks is completely alone as a black man.  In fact, he has had no visitors from the other men.  Lennie was one of the first people to visit him.  Curley and his wife have a horrible relationship, even though they have been married a few weeks. 

Within this context, George and Lennie has something special and amazing - companionship. 

Here is conversation between Slim and George that makes this point:

Slim looked through George and beyond him. “Ain’t many guys travel around together,” he mused. “I don’t know why. Maybe ever’body in the whole damn world is scared of each other."

“It’s a lot nicer to go around with a guy you know,” said George.

In conclusion, one of the main themes in the book is the friendship that Lennie and George share together. 

George has promised Lennie's Aunt Clara that he will watch out for Lennie, and he does this in numerous ways, constantly, in John Steinbeck's story Of Mice and Men.

As the men approach the water hole, George tries to protect Lennie from drinking bad water. We get the sense quickly that something is not quite right with Lennie because George has to explain very simple concepts to him, and Lennis forgets a lot.

We find out, also, that George had to make a run for it with Lennie, escaping and hiding to protect Lennie, when Lennie got carried away with feeling a young girl's dress (he loves soft things) and frightens her.

So [Lennie] reaches out to feel this red dress an' the girl lets out a squawk, and that gets Lennie all mixed up, and he holds on 'cause that the only thing he can think to do...

When the girl says she was raped, the authorities come after Lennie with men ready to lynch him, and George has to hide Lennie and then make sure they get away.

George watches out for Lennie when Curley comes in and starts picking a fight. He lets it go on for a while, but then tells Lennie to stand up for himself—to fight back. Lennie has no desire to hurt anyone, but in defending himself, he eventually crushes Curley's hand. Embarrassed, Curley explains to the others on the ranch that he got it caught in some machinery.

George tells Lennie how he should behave on the job. In particular, he tells Lennie to stay away from Curley's wife. Lennie remembers this clearly and tries hard to do as he has been told, but Curley's wife will not leave Lennie alone, and ultimately tragedy follows.

George also gives Lennie a dream—in essence, George has a dream and lets Lennie share it. George wants to own a piece of land with a house, and work the land. This also becomes Lennie's dream, as George tells him that he can care for the rabbits. Lennie is overjoyed.

In the end, when the men on the ranch chase Lennie to kill him for the accidental death of Curley's wife, it is George who takes Lennie's life, knowing how horrific it would be for the sweet-natured Lennie to face the anger of a mob and death at the hands of men with murder on their minds. It is just another way that George watches out for Lennie.

Lennie is a challenged friend of George's.  It would seem that George would be more important to Lennie but this can be seen two ways.  First, of course George provides Lennie with the opportunities to live a full life.  But, how is Lennie important to George?

These men spend their days traveling from ranch to ranch searching for work.  This is the only way they can escape poverty.  Interestingly, John Steinbeck worked as a farmhand in his early days to help make ends meet.  It is not surprising that this story is so realistic!

Lennie is George's only "family".  George has real meaning in his life because he has to keep Lennie safe.  Lennie is the soul of George's dreams.  Never once does George think of getting a house on his own.  He always considers the American Dream and how he and Lennie will someday save enough money to buy their own place so they can escape the hard life.  Lennie is George's reason to keep living. 

It is ironic that George has to make an almost impossible decision at the end of the book.  Ultimately, he makes a decision to protect Lennie until the end even when in doing so, he destroys his own future.

There are two reasons - 1) Lennie is a responsibility to George, and George takes that seriously.  2) Lennie is a companion to George.

George made a promise to Lennie's dying aunt to take care of him.  George is an honest man and a loyal one.  He will not break his promise.  We know this in the first chapter when he explains how hard it is for him having to care for Lennie:

I could go get a job an’ work, an’ no trouble. No mess at all, and when the end of the month come I could take my fifty bucks and go into town and get whatever I want . . . An’ whatta I got,” George went on furiously. “I got you!”

And yet, despite his anger, he won't give Lennie up.

The second reason is the companionship.  A major theme in this novel is that of loneliness and alienation.  The life of these migrant workers during the Depression was a sad one.  This is demonstrated through the "handicaps" of the characters - Lennie's intellect, Candy's hand, Crook's skin color, etc..  However, Lennie and George have a friendship these other characters don't.  This is why Candy wants to join with them in the plan to buy a little farm.  He wants to have a group, too.

"Guys like us, that work on ranches, are the loneliest guys in the world. They got no family. They don't belong no place....With us it ain't like that. We got a future. We got somebody to talk to that gives a damn about us."

These two men are united in their struggle to escape poverty, loneliness and hopelessness.  Although Lennie is mentally handicapped, he is a special friend to George, more like a brother. 

Lennie needs help because although he is a full grown adult, he has the mind of a child.  In addition to his child-like innocence, Lennie possess a powerful strength that constantly gets him into trouble.

George's life has more meaning because he acts as Lennie's caretaker, having promised his Aunt that he would look after him.  They talk and share a sweet, never-going-to-happen, vision of being their own bosses someday on a farm that they would own together. 

"George and Lennie dream of owning a farm, but by the end of the novel the dream has failed. Their plan is doomed because human fellowship cannot survive in their world and also because their image of the farm is overly idealized."

There is room for speculation when it comes to the relationship between Lennie and George in John Steinbeck's classic Of Mice and Men. What is meant by room for speculation refers to the rationale behind a friendship so awkward and made of two completely different personalities.

However, we can start by stating that Lennie and George are cousins, and apparently they are the only family each other has. While this is a good reason to suppose that Lennie was important to George, it does not completely answer to the question" "Why?" Yet, this is when speculation begins.

The first motif for their unconventional connection is that they are both loners. They live in isolation from the rest of society and each of the men, in their own unique way, finds it hard to connect with the world. Hence, they enmesh their relationship and look within each other to find that much-needed link to the community.

Second, because they are family and because they have made a form of bond, they look out for each other. In any case, George looks out for Lennie because he knows Lennie cannot not do it alone. After all, they ARE family, and they DO have that bond that secludes them further from the rest of the world.

Finally, Lennie must be important to George because he shares with George the same goal and hope: To own their own farm and move away from everyone. Just by sharing the dream makes the men more connected than ever. After all, they both share half of the dream. Without the two of them together the dream would not be completed.

These are some of the possible reasons why Lennie means so much to George: Their family bond, their common isolation, and their shared dream.

George does get some benefit from having Lennie as a companion. George is described as "a little guy," while Lennie is a giant with enormous strength. These two men are struggling to survive in a tough world. Lennie can offer George protection from men who might try to rob him or might pick a fight with him just because he is "a little guy." They have to sleep in boxcars and in hobo jungles. There were twelve million unemployed men during the worst years of the Great Depression. The world was a dangerous place for men who were unemployed and roaming the country looking for work. 

James M. Cain wrote a number of good novels about the Great Depression. The best-known of these books is Mildred Pierce. Cain's novel The Moth (1948) contains many chapters portraying the hard lives of hobos traveling all over America in freight cars looking for unskilled temporary laboring jobs.

Just as Lennie has great strength to compensate for his feeble intellect, so George has above average intelligence and "street smarts" to compensate for his small size. The two men have a symbiotic relationship. Lennie needs somebody to tell him what to do, while George can sometimes use a bodyguard. 

George and Lennie are the main characters in Of Mice and Men by John Steinbeck. George is a small, spare man and Lennie is a strong giant of a man who is also mentally challenged. People who meet the pair for the first time always wonder why George takes care of Lennie (because they can all see that it is rather a full-time job to do so). In chapter three, we hear George explain his relationship with Lennie to Slim.

Though we do not know all the details, we do know that Lennie was raised by his Aunt Clara and George lived in the same neighborhood. When they were little, George did not act as nobly as he does now, and he used to tease and torment Lennie just like everyone else. Despite that, Lennie grew attached to George, and Lennie finally quit taking advantage of Lennie for his own amusement once he discovered that Lennie was so loyal to George that he would literally do anything George told him to do. When Lennie's Aunt Clara died, George took over as Lennie's caretaker.

This childhood friendship has turned into a rare friendship, especially in the world of itinerant ranch hands. George may resent Lennie at times, but the truth is that he needs Lennie as much as Lennie needs him. George says:

“A guy needs somebody―to be near him. A guy goes nuts if he ain't got nobody. Don't make no difference who the guy is, long's he's with you. I tell ya, I tell ya a guy gets too lonely an' he gets sick.” 

The fact that George has not always been nice to Lennie makes their relationship even more believable and more satisfying now that they are adults. 

It is apparent from the very beginning of Steinbeck's Of Mice and Men that Lennie is mentally challenged. Steinbeck first suggests this when Lennie is quite pleased with himself after producing splash rings in the river where he and George stop in Chapter One. Lennie is also carrying a dead mouse in his pocket, symbolic of his childlike obsession with petting soft things. Lennie is also obsessed, like a child waiting for Christmas, with the prospects of "tending rabbits" on the farm which he and George hope to one day own. George is obviously Lennie's caretaker, making sure that Lennie eats regularly and has a job.

Lennie had originally been cared for by his Aunt Clara, but when she died, he went on the road with George. George makes important decisions for Lennie and in Chapter One, he is holding Lennie's work card, which will be used to work on the ranch where they are headed near the small central California town of Soledad. Lennie is, however, quite a handful and, although George genuinely seems to love him, he is often frustrated by Lennie's actions, such as the incident in Weed involving a girl in a red dress. Despite this, he cares for Lennie like a brother, mediating their first meeting with the boss and asking Slim if Lennie can have one of his puppies.

George also warns Lennie about interacting with Curley and Curley's wife. Unfortunately, Lennie is unable to avoid trouble, and his fight with Curley is followed by the episode in the barn when he accidentally kills Curley's wife. Even though George does his best to take care of Lennie, it isn't enough. In the end, he does what he believes is the most humane thing for Lennie by shooting him in the clearing next to the Salinas River in the book's final chapter.