I strongly suspect that there's a psychological phenomenon that no one has noticed, because no one *ever* mentions it, yet when I bring it up sometimes people say "Oh yeah, I had that happen."

Basically, it's people having an imaginary friend as a mentor during their teenage years, and here's what seems to happen:
The imaginary friend can just be a voice in the head, thoughts that happen without 'you' thinking them.
It is a distinct personality from yours, seeming smarter and more well-adjusted.
It helps you manage your angsty teenage emotions, and can give input unprompted.
It's not a symptom of any personality disorder or psychosis, it just exists as its own thing.
It eventually goes away; perhaps because it stops being needed, or because you're too similar to it after years of mentoring.

So I'm just curious as to whether it's a fluke with the people I asked, or if it's a real phenomenon and throwing the question out into the wild will net a few more "I had that happen" responses.
It could be that lots of people grew up with imaginary mentors, and no one's ever noticed because everyone thinks it's a weird personal experience they probably shouldn't mention.