Fiction gives writers leave to let our imaginations run wild and concoct a world of fantasy, where magic, true love and justice are as real and dependable as taxes in the non-fiction realm. However, there are some things that are acceptable in real life that cannot be sprinkled into fiction without a degree of caution; such as coincidences.
Coincidences happen every day. I was giving training where I needed to open my inbox for 30 seconds so I could show staff how to save an email. At the end of the session a girl came up to me and observed that we had both been invited to the same party by someone outside of my work life. We have been friends ever since. As if that is not coincidence enough, I sent an email to one of my friends who works in accounts when, unbeknown to me, she was training a friend of mine who had just started at her office. Both girls saw my email which broke down the degrees of separation to zero! So that coincidence has happened to me twice! TWICE! Yet I could never write it in a story because no one would believe it.
The only time that coincidences are slightly acceptable (but even here tread carefully) is if it is a bad coincidence. If it occurs at the beginning of the story and helps your main character find out her partner is cheating, or the world is about to end, or aliens are living next door, then that is acceptable. If it saves the day and prevents the tragic end to which the whole story has been geared, then you are going to find your book in the recycle bin.
One of the big rules of writing is do not pull your reader out of the story, and unfortunately, even though we have all had good turns of fortune because of them, a happy coincidence is going to rip your reader right out of your tale. So the coincidence is one facet of real life that generally can’t find a home in any genre, except maybe the memoir, and only then if it can be proven. We are a cynical bunch after all…