[aamar]

> Rigid hierarchy is generally not how the human mind works...

Jeff's sneaking a lot into the qualifier "rigid" here. The human mind loves hierarchies of many sorts, but most when the hierarchy is based on the context. For example: house cats could be mammals (near tigers) or pets (near fish).

A concept or object that is relevant to different contexts needs to show up in differently-organized hierarchies, or failing that, probably ought to be organized non-hierarchically (e.g. flat or "tagged"), so as to reduce cognitive dissonance.

Over-simplifying considerably, comments on Reddit/HN tend to be interesting mainly in just one context, so a hierarchy is probably helpful.