Have you ever heard the old expression that says “money can’t buy happiness”? Through the haze of glamour and all the extravagance of his party, Gatsby appears to be wondering at this moment whether it was all worth it and whether anyone actually cared about him. When Nick had been asking about Gatsby’s whereabouts earlier in the evening, nobody had known where he was, and Nick was made to feel as though he was actually asking a strange question. All the guests apart from Nick, it seems, were there for the party rather than out of any affection they may have felt toward Gatsby.

It should be noted, however, that it is not the approval of the “friends” at his party that would have made Gatsby happy. Gatsby believes having Daisy Buchanan would lead to happiness. Daisy, however, is married to Tom who, by the way, is having an affair with Myrtle.

Happiness is a commodity in short supply for most of the characters that Nick meets in the high flying world of East Egg. Jay is miserable without Daisy; Daisy is miserable in her marriage, as clearly is Tom, because he feels the need to keep cheating on his wife.

The “faint doubt” that Nick saw written on Gatsby’s face ties into the theme of materialism that prevails throughout this classic novel. It reminds us of materialism’s ultimate failure to provide happiness.

What this quotation illustrates is the fact that phenomenal wealth is no guarantee of happiness. On the face of it, Gatsby seems to have it all—a huge mansion, pots of money, and a luxurious lifestyle that would be the envy of just about anyone. But in reality, as the look of faint doubt on his face reveals, he's not really happy with his lot at all. And that's mainly because he doesn't have the one thing he really wants in life, which is Daisy Buchanan.

Without Daisy, Jay feels bereft and unfulfilled, as if there's a huge void in his soul waiting to be filled. A similar lack of fulfillment is experienced by many of the minted guests who show up at Gatsby's legendary parties. They, too, are stinking rich and lead fabulously opulent lifestyles. And yet none of them seem to be truly happy, either. Daisy certainly isn't, and as for Tom, if he's so happy with everything, then why does he always feel the need to cheat on Daisy with other women?

Gatsby's look of faint doubt, as well the general air of unhappiness that hangs over the lives of East and West Eggers alike, draw our attention to one of the book's main themes: wealth and materialism, and the gaping spiritual void at the heart of them.

Towards the end of chapter 5, Jay Gatsby is entertaining Daisy in his mansion after meeting her for the first time in five years. Over the last five years, Gatsby has recreated himself into a wealthy businessman in order to win Daisy's heart again. In Gatsby's mind, he envisions Daisy as the perfect woman in every sense of the word. However, Gatsby has created an illusion in his mind that Daisy will never be able to live up to or fulfill. While Nick Carraway watches Jay Gatsby entertain Daisy, he mentions,

As I went over to say good-by I saw that the expression of bewilderment had come back into Gatsby’s face, as though a faint doubt had occurred to him as to the quality of his present happiness. (Fitzgerald, 51)

Gatsby's "faint doubt" and appearance that he has questioned his happiness illustrates the theme of illusion vs. reality throughout the novel. After entertaining Daisy for the first time in five years, Gatsby is slightly underwhelmed. He has created an illusion of Daisy that cannot compete with her physical self. Gatsby's grandiose perception of his perfect, ideal reintroduction with Daisy falls short of his imagined scenario.

Throughout the novel, Fitzgerald explores how various characters create illusions in their mind to protect their emotions and motivate them to attain success. The theme of illusion vs. reality also corresponds to the theme of the American Dream. Essentially, Gatsby believes that he will be able to buy happiness, which is not the case. Similar to how Gatsby believes that his financial success will result in a loving relationship with Daisy, his illusion of Daisy's perfection does not equate to reality.

ABSOLUTELY this can serve as a theme for the book! If you are writing a paper about the American Dream or the purpose of Fitzgerald's work, you have selected a very effective quote!

Nick says this after Gatsby has restored his love with Daisy and Nick was getting ready to leave Gatsby's home after Gatsby showed Daisy all around it.

This quote demonstrates that once a person on a quest achieves their purpose, there may be a type of let-down. It's sort of like the fact that some people get in love with being in love, but not the person they think they are in love with. Teams work for district and state championships, and the journey is fulfilling, but once it's over, it's over. Now that Gatsby has Daisy he is no longer being fulfilled by the pursuit.

In this chapter, Gatsby has just managed to have his meeting with Daisy, to see her again after all these years.  They seem to have fallen in love all over again and so Gatsby ought to be happy.

In this quote, though, Nick is saying that Gatsby thinks that his happiness at this point might not be real.

I think this is a good quote to sum up the whole novel.  In this book, Gatsby spends his whole life chasing after something.  He is chasing money and prestige and Daisy.  But none of that stuff, in the end, actually makes him happy.  Fitzgerald is saying that all the things that people are trying to chase in this era, their American dreams, are really fairly pointless and will not make them happy.