Steinbeck shows that the treatment of Crooks is unfair in Of Mice and Men because he is treated badly due of his race.
Crooks is easily dismissed because of his back injury. He tries to be helpful, but he is often seem as not as capable. When Crooks tries to tell Slim that Lennie is playing with the puppies, he is basically ignored.
"Just thought I'd tell ya," said Crooks. "He's takin' 'em outa the nest and handlin' them. That won't do them no good." (ch 3)
Since Crooks is black, he does not have any freedom of flexibility. He is stuck on the ranch. His race makes him invisible, which makes him lonely.
And scattered about the floor were a number of personal possessions; for, being alone, Crooks could leave his things about, and being a stable buck and a cripple, he was more permanent than the other men. (ch 4)
When Curley’s wife comes in, Crooks is annoyed that she has invaded what little privacy he has.
"Well, you keep your place then ... I could get you strung up on a tree so easy it ain't even funny." (ch 4)
Because of his race. Crooks is lonely, just like Curley’s wife. However, he gets no respect from her either. They are both isolated, but she feels superior to him because he is black.