Zora Neal Hurston opens here novel Their Eyes Were Watching God with an incredibly lyrical metaphor:

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.

By making the metaphor specific to men, she creates a contrast to the inner life and dreams that women, such as her protagonist Janie Crawford, might have:

Now, women forget all these 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.

The distant ships metaphorically are the vessel that holds and transports our dreams. Men project into the distance or into the future a vehicle for the things they want. For many, those dreams are never realized, always remaining just outside one's reach. They buttress one's hopes until such time that one is too old to believe in achieving them. When that time comes, these old men turn from the dreams of their youth in sadness, bitterness, resignation, and possibly humiliation. The life of men is full of unfulfilled promise and disappointment such that most are eventually broken by the very aspirations that once upheld them.

Women, perhaps because their dreams are so limited by their position as as "mules" to their men, instead make selection between what they want and do not want to carry inside themselves as memories. This seems to refer to Janie's grandmother's advice about black men who pick up burdens the white men decree but then insist that black women carry those burdens as mules.

Women like Janie—women who refuse to be turned into animals like mules who cannot participate in pro-creativity—forget what they do not want and refuse to carry it with them. The hold on to and carry forever those things they do not want to forget. In Janie's case, the epiphany of the pear tree stays with her until the end of the novel as does the sweetness of her relationship with Tea Cake.

The way men had abused her mother and grandmother into her own existence, the way Logan wanted to make her a mule, and the way Joe wanted to make her voice silent and objectify her for his own prestige are all things Janie chooses to set down and not remember.

"Ships at a distance" are dreams that are out of reach. Hurston seems to be saying that men very often pursue things that look promising but are not within their immediate grasp. For some, the ship "[comes] in with the tide"—that is, chance works in their favor, and they attain that which they desire. For others, the "ship," or dream, "[sails] forever on the horizon, never out of sight." The dreamer never forgets the thing that he covets, but he never realizes the dream. Eventually, "he turns his eyes away in resignation," for he is too old to realize the dream.

All of the men in the novel embody unfulfilled desire. Logan Killicks, Janie's first husband, is a rather bitter man who expects his wives to occupy a place of servitude. His only real interest is in the maintenance of his small farm. Hurston is less explicit about what Killicks's dream is, if he has any at all. She implies, particularly based on Janie's mention of his advanced age, that he is a man who has ceased to dream altogether, which is what makes him less capable of loving Janie. Joe Starks, Janie's second husband, fulfills his initial dreams of taking Janie as his wife, then becoming mayor, but remains dissatisfied with the life that the two of them have built and takes out his frustration on Janie. Of all of the men, Tea Cake is most capable, like Janie, of enjoying what life can offer in the present.

Janie fits Hurston's characterization of how women dream. She envisions the life that she wants, then acts according to that vision. For her, life is not about the constant pursuit of objectives that remain out of reach; it is about the fulfillment of objectives that are compatible with her idea of happiness. Therefore, Janie has no problem leaving her marriages when they no longer serve her happiness.

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.