What does it mean that depth versus breadth in hierarchies?

Going deep in one branch versus wide across many branches are different strategies with different costs — and the right choice depends on whether you need resolution or coverage.

Example: You are reorganizing your notes on decision-making. You could create ten top-level categories (broad/shallow) — risk, bias, heuristics, frameworks, emotions, speed, reversibility, group dynamics, consequences, meta-decisions — and drop notes loosely into each. Or you could build three deep branches — risk (subdivided into probability, exposure, tolerance, mitigation, acceptance), bias (subdivided into cognitive, social, confirmation, anchoring, survivorship), and frameworks (subdivided into expected value, regret minimization, OODA, pre-mortem, second-order). The broad version lets you find topics fast. The deep version lets you think with precision inside each topic. Neither is wrong — they solve different problems.

Try this: Pick one branch of your personal knowledge system (a folder, a tag, a category). Count its depth — how many levels exist between the top-level label and the most specific item? Then count its breadth — how many items sit at the top level? Write down which feels like the bottleneck right now: are you losing nuance because everything is lumped at one level (too shallow), or are you losing orientation because you cannot remember what lives five levels down (too deep)? Restructure one section to fix that specific bottleneck.