Gatsby is dead; Myrtle and George Wilson are dead; Tom and Daisy have fled back West; and there's Nick, standing on Gatsby's beach and "brooding on the old unknown world" (9.150), thinking that we all chase after our dream, believe that one day we'll achieve it—and all the while, we're "boats against the current, borne back ceaselessly into our past" (9.151).
Way to send us off, right? This is a tricky passage, and we don't want to beat all the life out of it by offering you The One Interpretation. But here's what we think is going on: Nick realizes that chasing a future dream just ends up miring us in the past. All of our dreams are based on visions of our past self, like Gatsby who in the past believed that he would end up with Daisy and who believed in the American myth of the self-made man. By chasing these dreams into the future, he just ended up destroying himself.
And we think that this is a larger metaphor for post-World-War-I America. The U.S. is bound to a certain vision of its past—but what is that past? Is it a world that Gatsby believes in, a world where men can make themselves? Or is it Tom's world, where self-creation was always a myth, and what really matters is your family and your breeding?
One last question. Does this ending leave us feeling that there's a way to move forward—or, does looking to the future mean ending up like the only character who seems unaffected by the events of the summer: the hard, dishonest Jordan?