One of the major themes in John Steinbeck's novel Of Mice and Men is alienation and loneliness.
These are circumstances that Steinbeck addresses in this novel of the Great Depression, as well as his novel The Grapes of Wrath. After the Crash of 1929, people throughout the country were disenfranchised: jobs and homes were lost, work was impossible to find, and survival was an uncertain prospect.
People would often leave a place they had known for their entire life to try to find a better chance for work. Being on the road brought an overwhelming sense of loneliness and alienation. Work that was found might only last a short time, and would force people to move on again. Those on the move were not welcomed by those within communities that still had enough to live comfortably, often being met with suspicion or outright hostility.
Lenny and George are two of these kind of men. They move around not only because of their need for work, but also because Lenny, without malice, causes problems which prevent them from staying on in one place, if the work were available to them.
In the novel, George and Lenny speak of their situation.
'Guys like us,' George says, 'that work on the ranches, are the loneliest guys in the world. They got no family. They don't belong noplace.' Lennie replies: 'But not us. And why. Because . . . because I got you to look after me, and you got me to look after you, and that's why.' The alternative to the companionship that George and Lennie share is loneliness.
George and Lenny are not the only people that are lonely. It would appear that this is a sign of the times. Men they meet on the ranch where they stop to take on work are suspicious of the bond the two men share because so many are alone, and so few have companionship.
Lenny aggravates George with his unpredictable behavior and their need to constantly be on the move, but George still stays with him and watches out for him. He explains to others that they are related and that he has promised to keep an eye on Lenny. This helps to allay the doubts and suspicions others have about them. George may well stay with Lenny because the only other option open to him is to be alone.
However, when Lenny unthinkingly kills Curley's wife, George realizes he must make a truly difficult choice. On the run from the law, George quietly, and as humanly as he knows how, kills Lenny before the police can take him. Sadly, it's like putting down a rabid pet for George: in essence he protects Lenny from jail and perhaps execution, but in doing so, he finds himself once more alone.