What does Crooks try to make Lennie believe? Why?

Crooks teases Lennie about his lack of self-reliance; he tauntingly asks Lennie what he would do if George were injured. Unable to think hypothetically, Lennie thinks that George is actually under threat. With some difficulty, Crooks calms Lennie down and takes on a kindlier demeanor. His sour attitude remains, however, as he tells Lennie that his dreams of owning a farm with rabbits is unlikely to amount to anything tangible. Crooks tries to make Lennie see that the dream in unattainable because he, himself, doesn't believe it's possible. Not to mention, he's rather jealous.