Put a cat in a sealed box, Schrödinger said, with a gun that has a 50/50 chance of shooting the cat in response to an unpredictable, random quantum event. Because the box is built so solidly that no outside observer can get any information about what happened, then the cat is both alive and dead until someone opens the box and looks inside. Or at least, that's the dumbed-down version of the thought experiment, that's supposed to be simple enough to be comprehended by mere mortals.
The one part I've never understood, though, that seemed obvious to me even as a little kid, is how there is supposed to be any uncertainty about what happened in the first place. The cat being alive/dead is not the random event; it's an effect of the random event: the gun firing. And there's something outside of the gun that can observe it: the cat itself. So where does the uncertainty due to the event not having been observed come from?
(And yes, I realize that it's just an idea that's not meant to be taken literally, but if it's supposed to be an analogy that models a real problem, then ISTM it should be a model that doesn't have a hole in it that's so obvious a child can see it.)