Comment by antiraza

I'm not certain I understand where the problem is? Trades are learned by apprenticeship. Knowledge is learned by oral transmission. As the previous commenter said, this has been normal for most of history, and frankly is still the case many places around the world. Literacy is _new_. Even when literacy was emerging, it was likely that a mason or a carpenter was not of a literate class and they learned the same way generations before them did: apprenticeship and oral knowledge transmission.