You could think of this as simply reexamining one's premises,

That's exactly what it sounds like. Identify your AXIOMS.

but it's actually much deeper than that, because your premises could actually be supported factually, yet still miss an entirely different mode of being which bypasses your present mental world entirely.

"If just one of those things [new axioms] gets down here then that will be all, and all this, this, BS that you think is so important, you can just kiss all that goodbye."