Cogito, ergo sum...............Descartes
Introspection, or examination of one's own thoughts, has been a central focus of art, psychology, and philosophy. It's a primary element of consciousness. What's up with that?
Long time readers, if any, may guess that when I ask a question like that I'm probably looking for a Darwinian answer - what, I mean, is the evolutionary function of introspection? Any complex system that moves needs to have some information about its environment and its internal state, and especially of self and non-self. So far as I know, snakes don't actually make the mistake of swallowing their own tails. In a social species, it makes a lot of sense to have some capability for understanding the thoughts of others, and understanding one's own thoughts provides a useful template. When one's safety depends on successful inhibition of certain instincts, it makes sense to have a watchdog paying attention to instinctive and other responses.
Our introspection has access to only a very limited and often highly processed version of our brain activity - we don't experience the output of individual hair cells in the ear, or photo-sensors in our eyes, but highly processed syntheses of these. We see blue, not differential excitation of different types of cone cells. It could hardly be otherwise. Our consciousness only has room for a highly simplified model of our thought.
Jonathan Haidt compares our conscious, introspective, superego like "supervisor" to a small boy sitting on an elephant, trying to guide it. He has some influence, but most of the work is being done by the elephant.