I have heard some storytelling gurus state that the use of coincidence in a story is a heinous crime and should be avoided at all costs. Obviously Charles Dickens didn’t get that particular memo, as many of his greatest novels, including Oliver Twist and Great Expectations, contain all manner of fortuitous coincidences, many of which are integral to their plots.
My personal opinion is that if coincidence is used in a story, it must be done deliberately with a well-thought through reason. In the case of the Dickens novels mentioned above, the moments of coincidence have fabulist feel, ie the reader feels that they are reading a fable. As such using chance meetings or the like to turn the plot doesn’t seem out of place but rather an organic part of the storytelling process. For example in Great Expectations, when Pip discovers the truth about the relationship between Abel Magwich and Estella, it underscores the entire point of the fable regarding Victorian hypocrisy, the folly of class prejudice and our common humanity.
Outside of such stories, coincidence can be used, but is best kept to the openings – a chance meeting between two characters who then become lovers, for example. However stories that use coincidence later, especially if used to turn the final act, can feel forced, phoney and unsatisfying. This is particularly true if said coincidence comes in the form of deus ex machina, a poncey term for coincidence-zilla whereby a seemingly unconnected act of God gets the protagonists out of their trouble. Pixar’s legendary storytelling rules include “Coincidences to get characters into trouble is great; coincidences to get them out of it are cheating”.
One of my favourite Agatha Christie novels, Sleeping Murder, has a terrifically spooky opening that is entirely the result of coincidence. A young recently married couple on holiday in Devon just so happen to drive past a house for sale they rather like the look of. They decide to buy it, but as they go about various decorative renovations, a series of eerie discoveries sets the entire plot in motion, all as a result of the opening coincidence. But because it is the first major part of the story, the inciting incident if you will, what follows feels plausible rather than contrived, even though the odds of the couple coming across this particular house, which has ties to the woman’s past, must have been astronomical.
In conclusion, I think it is foolish to say coincidences (along with adverbs and – whisper it – passages that tell rather than show) are the work of the devil for writers. Instead, I see them as simply tools and techniques that should be used strategically and sparingly.