I'm curious about this. As I mentioned in another comment, I think the concept of hierarchy is somewhat difficult to understand initially. But it is a key abst

I'm curious about this. As I mentioned in another comment, I think the concept of hierarchy is somewhat difficult to understand initially. But it is a key abstraction for almost everything having to do with computers, and especially programming. Programming is all about understanding abstraction, at some base level. I don't know how many junior programmers I've encountered that look at source code and see it as a linear set of instructions, and just never developed the skills to abstract the problem first. Once you understand hierarchy, the world changes a little bit. The filesystem is a simple example, but often the first a person encounters.