I once wrote a novel inspired by coincidences. It was great fun–though hardly original. Metafiction, fantasy, fairy tales, and any number of other genres often require coincidence. Some even delight in riffing on it.
Often, though, we have to limit coincidence in fiction, particularly realistic fiction. Inexplicable interconnections and concurrences may seem contrived. Genre novelists—and Charles Dickens, for that matter—are routinely pecked apart for stories that are too perfect too be true, filled with dei ex machina and separated-at-birth twins reuniting on the altar or mothers rediscovering offspring on the other side of the world.
Even so, fiction often aims to tell the story of real life. And, real life is filled with coincidence, or at least what seems to be coincidence to unbelievers.