Right. But while I think the important point is about abstractions, it's still valuable to understand-about (even if not "remember in detail how to manipulate")

Right. But while I think the important point is about abstractions, it's still valuable to understand-about (even if not "remember in detail how to manipulate") the next lower level abstraction. Partly this is to fix things when the higher abstraction breaks. But TFA's point is to manipulate the system without bringing in the cost of the higher abstraction.