And of course someone can then ask: Why is that a really sad way to live?
Thus is the infinite epistemic loop.
There is no "root" in the field of epistemology - it's turtles all the way down. The French existentialists recognized this reality, and the response was: "make your own root and proceed from there." Ok fine, all that does is make the illusion more meaningful individually, it says nothing of the grounding of the illusion.
This of course means that we've only delayed the problem until the point when we meet other minds with different architecture - be it aliens, sentient AIs, or whatever. But that's kind of the point the whole AI risk movement has been making - that values and intelligence are orthogonal; there's no reason to assume that an intelligent non-human mind will automatically share values and moral intuitions with us.
Is it a trick of the brain? Are you simply forced to behave as if things matter when in reality you believe everything is pointless and nobody has any value beyond the hedonistic gratification they can provide you? If someone murdered everyone you cared about, would you claim that your grief stems from an illusion, a mistake?
You’re free to answer “yes” to all of these. I just think it’s a really sad way to live.