Once you leave behind the idea of “you” that is as an ego separate from everything around it you enter the unknown. The reason you enter the unknown is simply because you’ve surrendered to the Universe, the Universe moves through you, there is no I standing in the way, you’re an empty vessel. You have no expectations about this moment let alone the next moment. You’ve glimpsed the beauty that is the world and you trust the Universe completely.
The other aspect of entering the unknown is the simple logical conclusion that the ALL is unknowable. All we ever get is a limited finite conditioned view through consciousness. That which is infinite, unbounded and eternal is impossible to measure, beyond limits, and unconditioned. Space, time, and subject/object are all measures, all limits, all conditions of consciousness. Try looking at it this way; deep sleep or unconsciousness is merging with the ALL, and consciousness is a conditional experience of the ALL.
I’ve heard it said that the deeper our sleep the greater is our trust in the Universe, and in this context makes perfect sense. In Christian circles it may be called the cloud of unknowing. Like a deep fog, we are only ever a specific point, a light which illuminates only the immediate surroundings, fog is everywhere the light is not.