What is the importance of obsessions in The Great Gatsby?

The central obsession in The Great Gatsby is Gatsby's obsession with Daisy.  This is the reason for Gatsby's existence and for the novel.  It feeds the plot, the themes, the conflicts, the imagery, and the illusions. 

Daisy is obsessed with security, success, money.  Whether one sympathizes with her because she is a female trapped in a patriarchy, or condemns her for being greedy, the obsession is still central to her character.

Tom is obsessed with his stature, his place in society, his image, his success, and with maintaining the status quo.

These obsessions conflict and fuel the narrative.  Though figuratively all of these obsessions may be illusion, in the end, literally, Gatsby's obsession is proved an illusion, while Daisy's and Tom's obsessions survive.