Why is George so concerned about Curley?

George sees that Curley will be trouble in terms of Lennie. He has a complex about his size and needs to prove his strength and courage. Lennie's size and strength are a threat to Curley (yes, it's ridiculous), and he's bound to taunt and provoke Lennie before the novel's end. 

I am actually reading the book right now and i really don't know this question, my teacher asked us this question for hw