In the "The Great Gatsby", Notice how many times the author uses the words hope or dream. Why does he do this?

I haven't heard of "The Great Gatsby" so I can't tell anything clearly but my opinion, it's about the author. It may be because of something he lived before or living right then. Most authors have word(s) that they use frequently, i can't give any other example but you can even notice this in lyrics from the same writer's hands