Quantum superpositioning. Schrödinger was right, it's absolutely ridiculous and the cat can't be alive and dead at the same time, box or not.
The problem is it provably does work that way, or at least in a way that is indistinguishable from it, ridiculous or not, and we don't really know why. We've learnt many of the rules, managed to trap particles in superimposed states, even discovered that plants take advantage of it to transport energy more efficiently, and it's just a thing that happens, an apparently fundamental rule of existence. And it doesn't make any fucking sense.