It's an INTP survival trait. My understanding of the people around me is a bit analytical -- while I don't entirely lack the instinct for people, my intuitive understanding of social mechanisms is a tad weak, so I have to make up the gaps intellectually. And I've been applying that same analytical approach to my own head for the better part of 30 years -- not always successfully, but I usually have a pretty good semi-objective grasp of how I tick.

(I sometimes think of it as getting my ego out of my ego. It can be fun in a mind-warping kind of way, and fits extremely well with my increasingly Buddhist outlook on things...)