There seems to be alot of the comments here pointing out that the users are dumb, or they "just have to learn" – really? Aren't we the ones that should design solutions that are easy to understand, and easy to use?
It's a single basic thing users absolutely must learn. It's a foundation designers use to build their solutions upon. Every tool requires some prior knowledge to use it. You cannot use a spoon until you learned how to use it.
Hierarchical structures are natural to humans. Books with volumes and chapters, organizational structures, administrative hierarchies, etc, etc.
I defy the idea of people who "don't get" directory structure. It.. just cannot be real.
