To the contrary there is very good evidence that we pull arbitrary explanations whenever needed. See Gazzaniga's split brain experiments where people gave all sorts of reasons when asked why they did something and just could not know.
The fact that in extreme circumstances we pull explanations out of our asses (or even that we do so in non-extreme circumstances) doesn't mean we are incapable of genuine meta-cognition. No one is rational most of the times, but mathematicians can be rational for brief periods on limited subjects.
