What's the meaning of an element that belongs to the same element?

In classical set theory, if I consider that $x$ is an element, which means it is not a set, can I write $x in x$ ? If yes, what this would mean?
Correct me if I am wrong, but I don’t need to have some hierarchy here to apply the belonging operator, it means if I consider that exist a basic element, like the numbers, the operator is not only defined to the sets?