how is nick considered an outsider?

I don't know if I would say Nick is an outsider, but he is different. He was raised differently and embraces different values both socially and morally. He lives amidst the wealthy, but unlike his neighbors, he has the Egg without the mansion. Nick has a conscience, he doesn't take advantage of people, he has manners (doesn't show up where he's not invited), and he doesn't quite fit. Thus, for most of the novel we see him as an observer.... he's on the outside looking in.