As the narrator is watching the scene around him, as the "moon rose higher" and the "inessential houses began to melt away," Fitzgerald immediately jumps into an obvious extended metaphor of our human condition. When the true and pure light of the moon shone down on the world, the unimportant, and extra things that humans had added faded away from the narrator's sight. He saw the "old island" that was once there, the "fresh, green breast of the new world." When the push comes to shove, when the hard times and the piercing, yet subtle light of the truth pokes through to our innermost thoughts and emotions, the useless material things fade away, revealing the original base outline of our happiness, unclouded by materialism.
As the narrator broods, he thinks of Gatsby who "could hardly fail to grasp" his "dream," when all along, he had already moved passed his dream. That it lied in the past. His goal, his happiness, lied not in the accomplishment of his dream, but the mere concept of having a dream. The concept of hope, of having something to move toward is what Fitzgerald proposes is the true root of having happiness. Humans must always have a dream, a goal to work towards. A dream that lies "back in that vast obscurity beyond the city." The happiness that consists not of accomplishing our dream, but the happiness is in the concept of the dream itself.