The Great Gatsby is a great example of human dissatisfaction and the great distance one would go to satisfy and to feel complete. Gatsby's pocket was filled with money, his name carried fames, yet the girl of his dreams wasn't in his reach. Hence the incompleteness he had throughout the whole book.
First example of his incompleteness was early into the story, Gatsby likes to throw big and glamorous parties at his house. But his purpose wasn't what everyone's thinking, he only did it because he wanted Daisy to wander and somehow find his party. In fact, even Nick Carraway didn't know why he throw these parties until later in the book.