How does Fitzgerald use mistakes in perception to develop a theme in the last three chapters?

The American Dream is the idea that everyone should have equal opportunities Fitzgerald reinforces the idea of the American Dream through the characters in the book as well. By the last three chapters of Gatsby, we find that the American dream is merely an illusion. In fact, Daisy isn't real either. Gatsby's fantasy of Daisy is just as illusionary as the American Dream. In the end Daisy settles for abusive Tom over Gatsby because Tom's money is more secure. The hapless George sees Gatsby as his "enemy" instead of Tom. People who once flocked to Gatsby's parties have all but forgotten him after his death. Perception is a fickle thing in this book and so often it is clouded by illusion and delusion.