Gatsby's motivation comes from a love, deeply rooted within him, for Daisy. Also, throughout the book Fitzgerald keeps Gatsby an isolated character by his innocent approach to life's problems. This same type of innocence gives the book a bit of light in the gloominess of all the problems occurring.
First of all Gatsby's motivation is pretty obvious, Daisy. Other factors, like being fairly poor growing up or seeing Don Cody's extravagant wealth may have played their parts in Gatsby's desire for fortune. But for the most part Gatsby feels he has to exert himself to be everything that is above and beyond to win Daisy. All the extravagant parties he throws, his Rols Royce which Nick calls an "omnibus" for bringing people to his parties, he does all this just so Daisy might be caught in the web of it all. He has no desire to make himself known at his parties, he has no greedy self interest to better his image, and he even lets people meander with seemingly crazy ideas on how he obtained his wealth. Gatsby merely stays in the background constantly scanning all this in hope that his eyes might fall upon Daisy. "But it wasn't a coincidence at all Gatsby bought that house so Daisy would be just across the Bay (p.84)." After hearing this incite from Jordan, everything seems to fall into place. Gatsby's great house located just opposite of Daisy and his extravagant parties, not just frivolous actions, but happenings brought about by a deeply rooted motivation of one man's innocent love. .
Innocence, this is a certain something Gatsby has that no other character possesses. Gatsby seems to be blind to the horribleness of reality throughout the book. He goes so far to say to Nick, "Can't repeat the past of course you can!" The black and white childishness of this statement reveals just how simple Gatsby's ideals are. Before the war, he and Daisy we"re passionately in love, though the only thing keeping them apart was the fact that Gatsby wouldn't be able to provide the means for which Daisy lived and would have to continue living.