What explaination does Candy give George for Curley's treatment of Lennie?

Candy says that Curley feels like he has to prove something because he's a little guy. In order to prove himself, he picks on big guys purely because he's mad that he's not one of them.

The swamper considered.... "Well... tell you what. Curley's like a lot of little guys. He hates big guys. He's alla time picking scraps with big guys. Kind of like he's mad at 'em because he ain't a big guy.