What do the books in the novel 'The Perks of Being a Wallflower' have in common?

In general, they all have an outsider in them, or someone who is unique. Obviously, Salinger's Holden Caulfield is the ultimate misunderstood outsider teen, and Fitzgerald's Gatsby was always trying to fit into a certain world. On the Road is about Kerouac's "against the grain" ways, and then in Hamlet, everyone thinks he's crazy. You can go through this for all the works listed in some way :)