I'm often frightened by how spontaneously my brain seems to come up with something, because it could just as easily stop doing that and I'd have no idea how to fix it.
I once walked past a math book one of my friends had left open, glanced over, stopped, pointed to a formula, and said, "This is wrong." (Which it was.) I only did it that once, but it's the sort of anecdote you can tell for the rest of your life. And if my brain stopped doing that, I'd be screwed.