Hey look. There's an object on Mars that, from a certain vantage point, looks just like a squirrel. Must be a space-squirrel, right?
Wrong. Obviously wrong. There is a rock on Mars that, coincidentally, looks rather squirrel-like. Conspiracy theorists love coincidences like these because they come across as highly improbable, or even impossible, suggesting that they're not coincidences at all. But as Michael Stevens explains in the latest installment of Vsauce, coincidences really aren't that surprising, or even rare:
The upshot is that humans have evolved to find meaning in images, sounds and events, even when meaning isn't there (images of Batman, for instance, seem to show up an awful lot), and cognitive biases to reinforce the significance of these experiences in our minds.
Stevens covers a lot of ground in this characteristically excellent video, but he skipped one of my favorite cognitive biases, which just so happens to be the seed of many a perceived coincidence: The frequency illusion (aka the Baader Meinhoff phenomenon), when a thing you just found out about suddenly seems to crop up everywhere.