The opening lines of Their Eyes Were Watching God by Zora Neal Hurston are written as a metaphor for the novel, or at least for the protagonist, Janie.
Ships at a distance have every man's wish on board. For some they come in with the tide. For others they sail forever on the horizon, never out of sight, never landing until the Watcher turns his eyes away in resignation, his dreams mocked to death by Time. That is the life of men.
This is a complex metaphor for the dreams men have and their journeys to pursue them. Imagine looking out to sea and seeing the outline of a ship against the horizon; this is the vessel which contains all the dreams of man. Sometimes the ship gets closer and makes it to shore. This ship contains the dreams which come true. Sometimes that ship never gets any closer, it just keeps sailing back and forth across the horizon until the watcher's time runs out (he dies). That ship contains the dreams that never come true. This is the way dreams happen in life, as well.
It is interesting that, in the next paragraph, the narrator contrasts how women dream with how men dream:
Now, women forget all those things they don't want to remember, and remember everything they don't want to forget. The dream is the truth. Then they act and do things accordingly.
Christopher Booker makes the claim that every story falls into one of seven types, and this novel certainly falls into the "Voyage and Return" category. This story begins with the end of Janie's journey, and it is apt that Hurston uses a ship/sea/horizon metaphor to begin the novel. In fact, watch for the symbolic references to "horizons" throughout the novel, beginning with this metaphor.