I once found a professor of medicine to be under the impression that everything in mathematics is already known.
It's probably commonplace to hear that the masses labor under that misconception.
In some contexts, one is expected to cite authoritative sources to support factual statements. If one asserts that the belief that everything in mathematics is already known is widespread among the general population, are there authoritative sources one could cite to support that?
It seems to me that if one were taking a poll, it might be difficult to phrase a suitable question in a way that doesn't give away hints.