You've been fooled. We have ALL been fooled.
We were brought up in an education model that prizes knowing things.
If you proved in school that you know a thing, you got a gold star.
If you faced a list of ten things and proved that you knew 9 out of 10, we gave you a score and told you that it was good. We told you that if you knew fewer than 7 of the 10 things, you had failed.
The details, and the levels may vary, but don't get wrapped up in fascination about the margin of variance. The principle is, we taught you that knowing stuff was good and not knowing stuff was bad. We taught you that knowing more things made you better, and knowing fewer things made you less valuable.
We created a relationship to knowledge in our culture that prized knowing things as the gold standard, sometimes at the expense of understanding. Certainly, although we have sufficient means to measure understanding of a knowledge domain, we've failed to use those tools consistently, and we definitely missed the opportunity to place the emphasis there.