In John Steinbeck's novel, Of Mice and Men, one of the themes of the novel is loneliness and isolation. Crooks is both lonely and isolated.
The first reason is that he is a black man in a country rife with racial discrimination. He is not allowed to bunk with the other men because he is black, so he has a room to himself off of the barn where he fixes harnesses. At the beginning of section four, the reader learns that Crooks keeps to himself:
...Crooks was a proud, aloof man. He kept his distance and demanded that other people keep theirs.
At first it appears that Crooks does all he can to guarantee his privacy, and is happy with it. The other men go to town; Lennie sees Crooks' light and comes to his room; Crooks eventually lets him in. While Crooks talks to Lennie, it is hard to tell what his intent is. He gets Lennie upset by suggesting that George might choose not to come back or might get hurt while in town. Lennie would be alone; he gets very upset. Crooks insists that the plan George speaks of means nothing and will never come true.
However, Crooks changes the direction of his talk in admitting that it is hard to live such an isolated life with no one to talk to. Having a companion allows a person to keep his perspective, and he reminisces of how nice it was when he lived at home with his brothers.
Candy, who is now in on the plan, enters Crooks' room, and Crooks tries to act angry, but he's really pleased to have company. This indicates, again, how lonely and isolated he is. He starts to tell Candy that their plans are nonsense and will never amount to anything. Perhaps the dreams of others torment Crooks so that he tries to tear them apart. Candy insists that they're not far from taking that step because they have saved almost all the money they need.
Crooks has a change of heart and asks that if it comes about, might he be allowed to join them and work without getting paid? Candy seems fine with the idea, but then Curley's wife comes in. She, too, is lonely, looking for company. She starts chattering until Candy tells her she should leave. She will not, saying she could have had a better life, and how she doesn't like Curley. Again Candy tells her to go home; she refuses. Then Crooks gets up and tells her the room of a negro man is no place for her and she had better leave.
Curley's wife immediately goes after him like a snake chasing a mouse. She threatens him, reminding him of the power she holds over him. He shrinks into himself. Curley's wife has little or no power as a woman on the ranch, but she is white and is still more powerful than this black man. She threatens to have him lynched, and he becomes meek and respectful, while she rants on. Candy tries to defend Crooks, but she insists no one would listen to Candy either.
Candy says he hears the men, advising Curley's wife again to go. Eventually she does. George enters to collect Lennie, surprised to find him there. (No one goes in Crooks' room except Slim.) As George turns to leave, Crooks calls to Candy and tells him to forget about including him in the plan. Candy seems uncertain but agrees if that is what Crooks wants.
With one threat from the rancher's wife, Crooks is again reduced to a lonely, frightened man. Curley's wife has demonstrated that the American dream is not his. His life can be snuffed out simply on a word from her. The flash of light we saw in him is gone. Crooks' isolation and loneliness are greater than anyone else's in the book.