But then you’re just pushing the unknown/undefined part to “feels like”.
We cannot define it properly so we can’t discuss it formally or make assertions like it’s the only thing in the universe that is not an illusion.
You could assert “Cogito, ergo sum.” but that’s kind of been done before.
I thought “cakewalk” was a clever American amalgamation of “a piece of cake” and “a walk in the park”.
Turns out it’s actually related to slavery, so probably doesn’t count.