What is fitzgerald's real purpose in the great gatsby?

Simply put, the American Dream is the widespread notion that any American citizen can achieve happiness and fulfillment by simply working as hard as possible. Fitzgerald deconstructs this idea by showing that, though Gatsby works hard and acquires a vast store of riches, he does not ever achieve true happiness or fulfillment. For Gatsby, true happiness involves earning the lasting love of Daisy. However, though Daisy loves him in her own way, she is not able to love him as fully as he would prefer, and in the end Daisy abandons Gatsby. Thus, no matter how hard Gatsby works to gain material wealth, he ultimately dies alone, and so much of the novel's major purpose is to ultimately critique the mythology of the American Dream.