This might be way off, but I think the fly in the ointment is we don't understand human understanding. As noted by most, there is a difference in conscious vs unconscious understanding. Arguably, consciousness is just an extra layer of thought. Arguably, humans understand certain things without consciousness. So that means "understanding" has two definitions, and we tend to use them interchangeably. So that lets us move the goalposts around. Arguably, there are more than two kinds of understanding, each a different map of the active brain circuitry. Arguably, our conscious experience doesn't fully "map" these different maps for us, which suggests we don't understand our own understanding processes.

In short, don't we need to understand the human mind better (beyond our limited subjective experience of our understanding) before answering some of these questions?