Why do we roll our eyes?

When I’m exasperated, or mildly contemptuous of something, I look up at the inside of my (open) eyelids, without moving my head. “Eye-rolling” is an adjective to describe something particularly fatuous.

Why is that? This seems reasonable, except for the origin idea that we’re simply looking away from what we don’t want to see. I don’t really buy that.

Because you learned from the people around you that in your culture it is an adequate gesture to express exasperation.

It’s a learned gesture, same as nodding for yes and shaking for no.