How likely do you think it is that there might have been a person in a the last 2000 years who solved one of life's great mysteries but never reported/recorded it?

I think it's closer to accurate that life doesn't have a whole lot of "great mysteries", not counting frontiers beyond which we simply can't detect.

Instead there's just so much to learn, that it's impractical for any individual to learn even a modest fraction of it. But, there's usually some philosopher, or niche branch of medicine, or sect of monks somewhere or behavioral biologist or whatever that has figured out the answer to that particular question, and just nobody really bothers to ask them very often. And they only might know that one, just because they specialized in it. They won't know any of the others, just like everyone else.

Like, what is love could be a common one. But would you really say nobody knows, or just nobody starts knowing, but it is possible to figure it out, and rarely, some people do?