[blhack]

A lot of human knowledge cannot be written down and has to be passed on person to person. There isn't enough bandwidth in a book to actually convey a lot of it.

Machining is one instance of this. You basically have to have somebody show you how to do some of it. Same thing with forging.

(At least in my experience)

[vibrolax]

The difference between the most detailed written instructions and apprenticeship / personal instruction is instant expert feedback. Skills transfer can happen much faster when the loop is closed.

[tintor]

Not necessarily needs to be written down. Video is also possible.

[JasonSage]

The examples you cited can be written down and they don't have to be taught in person. You could instruct somebody to do these without being present in person. I'm sure there are reasons that's not the way it's taught primarily, but you've not convinced me it's fundamentally impossible.

[imtringued]

You don't need a complex example. Your first language is something that can only be taught by people who are alive. Even if there is a comprehensive textbook that teaches all languages you still have to learn your first language to read the book.

[DylanDmitri]

Good thing we'll have AR tutorials!