what is Gatsby's tragedy?

Answer 1

the above answer is good...

however, i think gatsby is also tragic because, in striving to attain something unworthy (daisy), he completely loses his own identity. He changes his name, his occupation, his lifestyle and tries to "buy" his way into upper-crust society. In doing so, whatever daisy may have once loved about him is effaced by his own denial of his former self. "new money" can never compete with "old money," and gatsby has to lose himself (and die) for this point to be understood.

Answer 2

It's right in the book, at the beginning of Chapter 1 :

"something gorgeous about him, some heightened sensitivity to the promises of life, as if he were related to one of those intricate machines that register earthquakes ten thousand miles away."

And Googling

Gatsby "green light"

I get :

"Nick compares the green bulk of America rising from the ocean [or how the pilgrims most have first seen America EVT] to the green light at the end of Daisy’s dock. Just as Americans have given America meaning through their dreams for their own lives, Gatsby instills Daisy with a kind of idealized perfection that she neither deserves nor possesses. Gatsby’s dream is ruined by the unworthiness of its object, just as the American dream in the 1920s is ruined by the unworthiness of its object—money and pleasure. Like 1920s Americans in general, fruitlessly seeking a bygone era in which their dreams had value, Gatsby longs to re-create a vanished past—his time in Louisville with Daisy—but is incapable of doing so. When his dream crumbles, all that is left for Gatsby to do is die."

"The Great Gatsby : Themes, Motifs & Symbols : Themes", Sparknotes : http://www.sparknotes.com/lit/gatsby/themes.html