I think the central theme in this book is loneliness and isolation. Everybody in the ranch is lonely. We meet Candy the old sweeper who only has his old dog as a friend. We meet Curly, the bosses son, who has a major case of small-guy complex. He is angry all the time and tries to goad Lennie into a fight. We meet Curly's wife who is so lonely that she drifts from cabin to cabin in the guise of looking for her husband. In reality she uses her sexual prowess to get a reaction out of the men. She is so lonely and insignificant, Steinbeck does not even give her a name.