One of the things that separates humans from the rest of the animals is our ability to recognize patterns. Our brains just love to sort through seemingly disparate, random things and make sense out of them.
It was important for our hunter-gatherer ancestors to be able to discern food sources camouflaged against the background, or tell a poisonous plant from a healthy one. Now, we have those weird magic eye posters that — if you unfocus your eyes just right — you can find an image of a sailboat or a frog or a rocket ship popping out of.
Unfortunately, there are times when our brains are a little too good at finding patterns, seeing them when they’re not really there. Think of Rorschach inkblot tests, for example. There’s no real pattern to them, but your eyes can pick out something recognizable all the same.