Coincidences are a terrible storytelling device.
Seriously. In storytelling, coincidences are nearly always lazy, cheap, and frustrating. A storyteller’s job is to tell a believable story, and few things are less believable than convenient twists of fate.
Coincidences are an easy way to keep a story moving or set up exciting events, but not a compelling one. A character stumbles upon an important path, clue, or MacGuffin by accident. Complete strangers end up sharing some implausible connection. By blind luck, a character overhears a conversation relevant to the plot. These plot devices are all pretty common in fiction, and also pretty lame.
Whether from desperation, inexperience, or laziness, storytellers resort to all kinds of cheap ploys. I’m as guilty as anyone. I’ve used more lousy coincidences in my stories than I care to admit.
What exactly are the problems with using coincidences in storytelling?
Well, since I asked….
Coincidences are cheap.
The major events in a story should be earned. They should be built up carefully; foreshadowing beforehand, or explanations afterward, can be helpful. Coincidences are an easy shortcut, and a cheap way to keep the story moving.
Coincidences damage the audience’s suspension of disbelief.
Suspension of disbelief is a fancy term for the acceptance of fictional events. If I suspend my disbelief in, say, talking animals, I can watch The Lion King without constantly saying, “Hey, that lion is talking. That isn’t realistic! Lions don’t talk. This is stupid.” Some degree of suspension of disbelief is necessary for nearly any kind of story.
Coincidences make it seriously hard to believe a story; they damage the suspension of disbelief. An audience might be able to swallow a fantastical tale of magic or spaceships, but a story with too many unexplained or convenient coincidences is too contrived to accept.
Coincidences are clichéd.
I already mentioned a few common categories of coincidences in fiction: the overheard conversation, the important thing discovered by accident, and the hidden connection between unrelated characters. You have probably seen some of these before. I know I have.
Coincidences should be avoided whenever possible, if only because they have already been done to death.
Sometimes coincidences are unavoidable, or the only alternative is something even more implausible. That’s fine. Minor or infrequent coincidences may stretch plausibility, but not destroy it. A story may even offer an explanation for apparent coincidences, such as a guiding hand behind the scenes. At the very least, lampshading (i.e. acknowledging) a coincidence can make it a little easier to swallow. Coincidences do happen, after all!
In conclusion, though a good story may include coincidences, it should never depend on them.