I can thank Donald Rumsfeld for the term "known unknowns." Indeed, there are known unknowns. That much I know, though I can never show it to you.
But think about this. Thoughts come as perceptions. They are perceived.
The perceiver cannot be found. Whatever is located when searching is only another object of thought. Perception remains, out of reach as that which is aware of the search and the thought object.
To establish a model for discussion, consider this. We cannot see black holes but we can see the gravitational lensing they cause around astronomical objects. Black holes are inferred phenomena.
We cannot see perceiving but we know perception is going on, so we infer it.
It comes under various labels, awareness, consciousness, being, non-physical reality, God. Since it cannot be understood, some will argue that they choose one label over another because it carries less mental baggage or because that is the only way an understanding can be approached by them.
Brain science now offers corroborating evidence for the absence of a self that perceives. A neural correlate of the self cannot be found, and instead neural feedback loops and "cross-talk" between brain areas explain how we walk, talk, think, and act. I will say this: Self exists only virtually, an effect of our search. It is an identification in the brain. This also, which is very important: The belief in self can be powerfully diverting and keep us mired in suffering. This view is basic to Buddhism and Advaita Vedanta, a Hindu teaching. Having said that, I will add that complete disidentification does not occur nor is it desirable as we need it to navigate through our challenging lives. There is, however, a release, a freedom, that comes from seeing through it.
As for consciousness, it cannot be located by brain science but a shift in it can relieve suffering. In his famous and classic 1974 essay, "What Is It Like to Be a Bat?" Thomas Nagel argues there is something that it feels like to be a particular conscious thing. Your taste of coffee or an apple feels like something materialist science cannot explain. But it can be inferred, albeit non-scientifically. A blind bat uses echolocation to fly, and we can never know the experience. A colorblind scientist can spend her life studying color vision until she is a world renowned expert and she would still remain colorblind.
Quantum physics has led us to the edge of the materialist scientific model and now Hugh Everett's multiverse has become increasingly acceptable as an explanation for the wave function collapse, a phenomenon physicists have tried to explain since the 1920s. Not a single universe, but a multiverse, or many universes. To paraphrase Hamlet, there are more things between heaven and earth than are dreamt of in the materialist model.
What comes next may seem paradoxical, but only because words have their limits. So here is also what I know.
"I" am the unknowable. Call it being, my term of choice. You cannot find being, yet you know you are. It is a known unknown.
Behind perception is a known unknown. Behind it is that which perceives, rather like an eye looking but unable to see itself.
Which brings me to consciousness, for perception is its function.
All perceptions are creatures of consciousness. As its creature, the perceived is an object of consciousness. As an object, the perceived can only be known in that manner. Consensus has the objective world as reality, but it is not. It is not because we cannot separate it from the perceiver. It is dependent on perception, not on itself. Hence consensual reality is is only that--consensual.
In the millennia before artificial intelligence, Eastern spiritual traditions called the consensual world illusory, but virtual is a better description. It is virtual reality, because like computers it contains data that can be processed. We use it and behave according to it.
Virtual. Mind events are mental objects, not objectively real. We do not instantly see trees by sunlight. Trees are illuminated by light from the sun that took eight seconds to reach them. My optical system encodes only part of light's spectrum. The tree is turned upside down and reversed on my retina, and in an "X" pattern the left image runs to the right brain, the right image to the left, and then is turned right side up after it reaches my occipital cortex, with a delay in time before consciousness registers it.
I live in virtual reality. This is a modern phrase for what the Buddha taught, what you find in the Hindu Vedanta, what Ramana Maharshi said. The Heart Sutra says form is emptiness; emptiness form. In Advaita Vedanta the seer and the seen are one. Ramana Maharshi put it succinctly: "Existence or Consciousness is the only reality. Consciousness plus waking we call waking. Consciousness plus sleep we call sleep. Consciousness plus dream, we call dream. Consciousness is the screen on which all the pictures come and go. The screen is real, the pictures are mere shadows on it."
To see it all as virtual is the trick, and I won't go into that here. You can find tons of offerings elsewhere. Cyberspace is full of nondual advice and self-praise on how the seeker became a finder. (There are also those who have truly found.)
I call it coming undone, you can read about it elsewhere, and the undoing can be done, however strange the phrase. This article may confuse some but I assume if you have read this far you know what I am about. If not go here and here for starters.