In this book the main character, Jay Gatsby, embodies the American Dream of the 1920’s. He is a wealthy, successful, young man that has achieved this greatness through hard work and effort, or it seems like that at a first glance.
Despite Gatsby having everything that is considered necessary to be happy, it is later revealed he is pretending to be someone he is not to impress the girl of his dreams, Daisy. Through this duality in Gatsby’s personality, we can see the opposition between dreams and reality. For he decides to become a successful wealthy man to obtain what he wants, but the reality is that by pretending to be great it is still impossible for him to go back time to achieve his goals.
This is furtherly explained in the video below.