<i>I see a pattern emerging, but is it a trick of the light?</i><p>I think it is fundamental. A hierarchy forms naturally from iterative steps of aggregation and differentiation: first, group all similar objects together; then, for each high-level group, look for differences within each group, and split the groups into smaller subgroups. Rinse and repeat until you&#x27;ve reached an acceptable number of items per group.