You ever see a dog that’s got its leash tangled the long way round a table leg, and it just cannot grasp what the problem is or how to fix it? It can see all the components laid out in front of it, but it’s never going to make the connection.
Obviously some dog breeds are smarter than others, ditto individual dogs - but you get the concept.
Is there an equivalent for humans? What ridiculously simple concept would have aliens facetentacling as they see us stumble around and utterly fail to reason about it?
This is a paradoxical question with no possible answer. If we’re to dumb to grasp it, how could we possibly know that it is in fact simple? Quantum mechanics may well be “the simplest thing” for an alien race, yet none of us would think our inability to fully comprehend it is a sign of stupidity.