The greatest struggle in "Of Mice and Men" is the struggle for a place in nature. This greatest of man's efforts to overcome loneliness and the economic injustices is a struggle that is universal to all men. In the novel it is exemplified by Crooks, who is made to live outside the ranch house away from the other men. He tells Lennie and Candy,
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.
Candy, the old man whose beloved dog is put down, knows that he, too, will be discarded when he can no longer function. Like Crooks, he will be isolated from the community of men where he has found some companionship, especially with his dog. His struggle to convince Carlson not to kill his dog is pathetic: To Slim with his "God-like eyes" and ears that "heard more than what was said to him" Candy
looked a long time ...to try to find some reversal. and, Slim gave him none.
Candy's old dog is taken out and shot by Carlson. Candy stares at the ceiling, powerless and isolated from all the others, not realizing that Slim has understood that if Candy were to keep the aged dog on, the other men would have turned on him. No dreamer,Slim is a doer. Yet, he does have compassion as he tells Candy that he can have any of the pups his dog has had. He also has Carlson bury the dog for Candy. Later in the narrative, it is Slim who consoles George after Lennie is dead: "You hadda, George. I swear you hadda."
One conflict in the novel that takes place between two characters is the hatred that Curley feels toward Lennie. From the very first time that Lennie is introduced to him, Curley is immediately intimidated by Lennie's size. Because Curley is a smaller man, he feels overpowered by how big Lennie is but is a man who can not handle being overpowered by anyone. The conflict is really not resolved until George kills Lennie at the end of the novel after Lennie accidentally kills Curley's wife.
Through this conflict, we learn that Lennie really does not have any idea of what is going on in his life or in the world around him -- his naivety shines through when you realize that he has no idea that Curley hates him. Additionally, you do find out just how strong Lennie is when he crushes Curley's hand out of anger toward him. The reader finds out that Curley is insecure and must be in charge and have total power no matter what.