At the conclusion of the novel when Henry Gatz shows up to attend his son's funeral, he brings with him a book that Jimmy Gatz had owned as a boy. In the book Nick finds notes the boy had made. There was a daily schedule and a list of "General Resolves." The contents show that as a boy, Gatsby had developed a plan to achieve the kind of life he longed for. His notes suggest discipline, hard work, thrift, self-improvement, and entrepreneurship ("Study needed inventions," said one note.) They also show a conscience: "Be better to parents."
When he could no longer stand being at home, Jimmy simply ran away, and his plans were left behind. He followed no particular course of action; he moved from one insignificant, temporary job to another, simply falling into whatever the moment offered. He attended college briefly and worked as a janitor to pay his way, but soon tired of it. He was too restless to stay in one place for too long, with his dream calling him on. By chance, he met Dan Cody, put on his new name, and became Jay Gatsby--sailing the world, living among the rich, and developing a pseudo-sophistication. It was chance, again, that threw him into the path of Meyer Wolfsheim, and his criminal association with the gangster led to Gatsby's great fortune.
Jimmy Gatz had dreamed of a life of beauty, glamour, wealth, and excitement. Jay Gatsby achieved that dream. However, when he met Daisy in Louisville before going to war, Gatsby's initial dream took a left turn. After that, Daisy became his dream and he dedicated the rest of his life to winning her back and repeating their past.
Once he had become wealthy and bought his mansion in West Egg, Gatsby learned that Daisy lived across the bay. At this point he did make a plan to bring her back into his life. He threw extravagant parties, hoping that she would "wander in" some evening. When he learned Nick knew Daisy, Gatsby arranged for Nick to invite Daisy to tea so that they could be reunited. Before the meeting, Gatsby went to enormous efforts to make the setting perfect for Daisy's appearance. He and Daisy did meet again, their love was rekindled after years of absence, and Gatsby's dream seemed very close to fulfillment. It was not fulfilled, however, and Gatsby paid with his life for pursuing it.
Gatsby's dream of Daisy was founded on illusion--the primary illusion being that only money separated him from Daisy and her world. It failed because it was rooted in illusion rather than based on reality. In reality, no matter how much money Gatsby possessed, he would never belong in Daisy's world. He lacked the social credentials; new money would never be as good as old money. Furthermore, as an outsider, Gatsby did not understand Daisy (an insider) and the forces that had shaped her and that continued to drive her. His dream of Daisy failed because it was an impossible dream to begin with, despite its "colossal vitality."