In chapter 6, Gatsby reveals his audacious dream that once he and Daisy are reunited, he can erase the last five years and start over as if nothing had intervened. It would be as if he had never gone to war and she had never married Tom. Their reuniting would represent a seamless resumption of their wartime romance, but this time with it coming to full fruition.
When Nick tells Gatsby he can't repeat the past, Gatsby refuses to believe it and tells Nick, "Why of course you can!"
Gatsby goes on to say:
"I’m going to fix everything just the way it was before," he said, nodding determinedly. "She’ll see."
Nick then recounts that
He talked a lot about the past and I gathered that he wanted to recover something, some idea of himself perhaps, that had gone into loving Daisy. His life had been confused and disordered since then, but if he could once return to a certain starting place and go over it all slowly, he could find out what that thing was.
Gatsby wants Daisy not only for herself but to renew some feeling he had about himself five years ago that was lost when they separated. He hopes to make right whatever has gone awry since their parting by returning to the unspoiled point of origin and retracing his steps, this time with Daisy at his side.
Nick will liken this to the first sailors from Europe who saw a new, unspoiled continent in America and were determined to start over and correct everything that had gone wrong in Europe: Gatsby's dream, in microcosm, is nothing less than the American dream.