[Confusion]

No blacksmith, farmer or famous scientist/artist/Renaissance man in history has ever known everything there was to know (about the field they worked in). Even back then, there was already more knowledge being produced than they could possibly ever obtain. As with us, the ultimate problem is a lack of time. Whether the time required to travel to a neighbouring city to learn from their guild or the time required to read a paper on the internet, the problem is time.

All stacks have always been too complex. A farmer, to produce optimally, has to understand everything there is to know about meteorology, biology, sociology, economics and earth sciences concerning his specific area. That has never been the case.

In that sense of 'understand', nobody has ever completely understood any system they worked with/in. Given a system and a person, you can come up with a legitimate detail question about the system that you also believe the person couldn't answer.