There are different theories about that but one prominent theory, namely, Freud's - that repression and resistance are the reasons why much of our mental life is unconscious and save for himself -- he thought ordinary human beings could not break through that resistance on their own. As usual, Freud overstated things a mite, but there is something to be said for the view that we need some help in understanding the meaning of what is beneath the waves of our conscious lives - but that joint effort requires the ability to tolerate vulnerability and anxiety.

Good question! For what it is worth, it feels to me like the I. Freud would call "it" the observing ego. Kierkegaard famously stated "the self is a relation that relates itself to itself". So Kierkegaard would say it is the self and the self is a process. Surely, the labcoats would contend that this executive function is a bit of brain circuitry. But whatever you want to call that internal voice/ perspective on the self, it is something that next to everyone struggles with. The desire for peace of mind is pandemic and by that we usually mean freedom from whatever it is that watches the mind and passes judgements on our thoughts and feelings.

I believe that this is about as basic a question as asking, "What is being?" There is plenty of discussion about the causes of consciousness and different forms of consciousness but what is 'it' ? Awareness? But what is awareness? Consciousness is often thought of as a kind of light. Seems to have some connection with attention. Phenomenologists long ago pointed out that consciousness is intentional - that is, always refers to something beyond itself. Heidegger limned it as a kind of opening in being. I can't even imagine what a definition of consciousness would amount to. The great William james described it in terms of our ability to introspect - as in we are conscious of what we can introspect upon. But that is about as far as I can go in making myself conscious of the nature of consciousness. Thanks for a great question.