Why does nested structures fail?

The most common reason nested structures fails: Treating nesting as a property only of 'organized' or 'technical' domains. You think 'sure, file systems are nested, but my ideas are just flat.' In practice, every time you say 'that is part of this' or 'this is a kind of that,' you are invoking nesting. The failure is not that your thinking lacks nested structure -- it is that you have not made the structure visible, so you navigate it by feel instead of by map.

The fix: Pick any concept you work with regularly -- a skill, a project, a domain of knowledge. Write it in the center of a page. Above it, write two super-concepts it belongs to (the larger wholes it is part of). Below it, write three sub-concepts it contains (the smaller parts that compose it). Then pick one of those sub-concepts and repeat: two levels up, three levels down. You will find that the nesting does not stop. Every concept you touch has both interiority (things inside it) and context (things it is inside of). Map at least three levels in each direction.

The underlying principle is straightforward: Any concept can contain sub-concepts and belong to a super-concept. Nesting is not a feature of special data structures -- it is a universal property of how meaning organizes itself at every scale.