One problem is that the LLM's own knowledge, or lack of it, doesn't follow from any individual training sample(s). Even if there were a bunch of "I don't know X

One problem is that the LLM's own knowledge, or lack of it, doesn't follow from any individual training sample(s). Even if there were a bunch of "I don't know X" samples in the training set, that ought to be trumped by one authoritative "X is ..." one. The next problem is that the LLM doesn't know how reliable it's various training sources are (unlike a human who might trust personal experience > textbook > twitter comment), or even which samples come from which source so that it could learn that.