Just a Coincidence

The problem with fiction, it has to be plausible. That's not true with non-fiction.— Tom Wolfe

Real life is full of weird coincidences. Everyone has at least one story about an improbable convergence of good or bad events in their life, and has seen well-documented examples of strange coincidences in the lives of other people.

Fiction, however, requires an internal logic in order to keep credibility with the audience. In many ways, fiction is a more distilled way to process life experiences, cutting out the random and extraneous and focusing on the largest conflicts. So peppering your story with coincidences is often a way to completely destroy your audience's suspension of disbelief. It can also feel highly contrived if the coincidences take the place of credible action to move the plot forward, or completely change the tone and pace of the story (if plot twists drop out of the sky with no buildup).
There are some situations where a coincidence is okay as a plot device:

In the beginning. It's completely reasonable to use a coincidence to kick off the story, as long as the action unfolds causally from that point. In a small pool of characters. It's highly probable that, say, your doctor hero who specialises in hand surgery could bump into your main hand-surgeon villain at a conference, or that they went to school together, or the like. Similarly, in a country with a small population and large extended families, the probability of two characters being related or knowing each other is fairly high. It's a nasty plot complication. The caveat is that this does need to be hinted at-- if a meteor strikes unannounced in the middle of your spy drama, it comes off as an ass pull. However, if there have been murmurs about a potential tropical storm building, it is definitely allowed to hit at the point least helpful to your characters. In comedy. Comedy, especially stories with an absurdist bent, can tolerate a degree of randomness or coincidence that would cause problems in a more serious work. If there's an overarching reason. The Hitchhiker's Guide series, which includes some of my all-time favourite sci-fi writing, introduces the Infinite Improbability Drive, which actually creates absurd and improbable coincidences around itself. One could also have a supernaturally unlucky person, a superhero who manipulates probability or the like.