Nick and Gatsby two opposing facets of Fitzgerald's personality?

I had to read The Great Gatsby over the summer for my english cl and i'm supposed to write a two page essay on this question and I need a little help :) It kinda has a little to do with Fitzgerald's history so..if you don't know anything at all about this guy you probably wouldn't be able to help me out.. Anyway this is the question: Some critics have suggested that Nick and Gatsby represent two opposing facets of Fitzgerald's own personality and that the battle within him between these two opposing elements contributed to his personal tragedy. What two kinds of personalities do Nick and Gatsby represent?