You, seeing this, are experiencing sensation.

You, reading this, are experiencing complex cognition.

However it may be that the universe is arranged, there must be something that undergoing those experiences; there must be something, somewhere in reality, that is what you consider to be yourself.

This is knowable as a perfect truth. There’s no way to be certain you aren’t in the Matrix, or that you aren’t an entirely simulated consciousness, or that you aren’t an alien having an exceedingly realistic psychedelic drug trip, or that you aren't just a random set of particles interacting by arcane and unknowable rules in a void, which by random chance has them arranged in a way that renders them temporarily capable of cognition.

But you can be certain that there is a thing that sees itself as you. Cogito, ergo sum.

This may well be the most elegant and unassailable argument ever constructed in the history of humanity.

Come what may, in the pages and years alike to follow this moment—it may be that there is no self, or agency, or choice. But it is absolutely true that there is experience, and thus there exists absolute truth.