Russell's paradox

Russell's paradox is a weird thing that happens when you try to think about sets in a certain way. A set is a group of things, like a group of apples, or a group of people, or a group of numbers.

Russell's Paradox talks about a special set called the "set of all sets that don't contain themselves". That means any set that is not a part of itself. For example, if you had a set of all blue apples, that set would not contain itself because it isn't an apple, it's a set of apples.

Here's the weird part. If you try to think of this weird set that's made up of all sets that don't contain themselves, is the weird set a part of itself? If it's a part of itself, then it isn't a set of all sets that don't contain themselves. But, if it isn't a part of itself, then it is a set of all sets that don't contain themselves.

So, no matter what you decide, the answer doesn't make sense! That's Russell's Paradox.