The fact that I can be aware of my own thoughts is preposterous. How is it possible? Is my cup aware that it is a cup? Is the coffee aware that it is hot and brown? Of course not.
Why should I be aware of what I am thinking? That is not reasonable. Nor could it have been predicted by any scientific observation. It is utterly perplexing.
There are many philosophical and quasi-scientific explanations of introspection. One is to deny that introspection is actually a fact. That eliminates a large anomaly from the purview of the scientific explanation of the world, but at the expense of self-contradiction. Introspection is required to understand what is being denied.
Another explanation is that one part of the brain becomes aware of another part of the brain, so really, introspection is just brain activity, completely physical. Beside the awkward fact that there is no scientific evidence for this hypothesis (nor could there be, since “awareness” is not a scientifically defined function of brains), this proposed solution does not answer the original question. I am a person, not a brain. It is I who have the introspective thoughts. If my brain also does a little introspecting on the side, so be it. Perhaps my liver introspects also. It wouldn’t matter to me.
What if we set aside self-contradictory and confused biological explanations of introspection, and consider only the mental experience? What is the experience of introspection?
We don’t introspect every minute of every day. On the contrary. Most of the time we are focused on the world, not on our own thoughts. But when we are focused on our own thoughts, what is going on? Who is focused on what? If I am the thoughts, who is looking at them? If I am the witness to the thoughts, who is in charge of the thoughts? I am pretty sure there is only one me.
This is one of the most profound mysteries confronting humanity.