In The Great Gatsby, the last sentence reads:
So we beat on, boats against the current, borne back ceaselessly into the past.
This refers to the dualities of Gatsby and America.
At the end of the novel, Nick aligns himself Gatsby. Nick says Gatsby is worth the whole damn bunch (the Buchanans and Jordan, et al) put together. So, Nick is saying he will get into Gatsby's boat, the one that only sailed backwards on the sea of history--into the past to recapture his childhood dreams. Why do you think Nick goes back to his home, the Midwest and narrates the entire novel from there? It's an idealistic, quixotic quest--both Romantic and hopeless.
Gatsby looked like a Romantic hero to Nick: he was a self-made man, a rags to riches story, a symbol of the American dream. But, when Nick get close enough, he saw that Gatsby was illegitimate. Nick found out that Gatsby used any means necessary to try to repeat the past.
Earlier, Nick paraphrases Gatsby's story of falling in love, perhaps for the first time, and the last time, when he met Daisy. Since then, Gatsby admits, his life has been disoriented. This is obviously before World War I, when he (and America) was young, boyish, innocent, idealistic, and romantic.
Gatsby is symbolic of America: his innocence in America's. Daisy is symbolic of his past. His longing to return to his past is akin to the Lost Generation wanting to recapture their lost boyhoods. Since then, they've lost their identities over on the battlefields of Europe, while rich kids (Tom) stole their girls (Daisy) back home.