Uh-huh! Well, Shadows are, anyway. Personas aren't, because the people who can use them are only the ones who have the potential in the first place. Even then, it's extremely taxing on their psyche, so they have to be able to handle it.

It's... actually really complicated! But... hm... how would I explain this to a regular person...?

[ He ponders, unaware what he's just said. Not that it bothers him. ] Shadows are the suppressed sides of people; the ones that they deny given form. They've been around for as long as people have.