I have no memory of a time when I didn't think self-reflexively, I'm pretty sure I was doing it as far back as kindergarden. Though I'm not sure I took it to the extremes of some of you, I only ever did modest personality modification :). I realized I could like any previously hated food just by trying. It's somewhat useful having such great control over thoughts and emotions. Like I've amplified my fear to help me in facing the feared situation (this might sound nonsensical, but it really works). In 6th grade I was confused when the teacher talked about what she called "metacognition" because I had assumed everyone did it all the time.
These sorts of ideas don't show up much in fiction, but has anyone read "The GamePlayers of Zan"? For example: one of the characters erases her own mind at the start of the book.

Cassandra: I was especially interested in your post because of certain ahem similarities to myself. (I'm really sorry if that link's too personal). We seem to think quite similarly. In fact everyone here does, I really need to stop lurking and start posting.