How do I practice edge cases?

The most direct way to practice edge cases is through a focused exercise: Pick one category system you use regularly — your task labels, your filing structure, your mental model of your team's roles, or your definition of 'done.' Find three items that don't fit cleanly into any single category. For each, write down: (1) which categories it partially belongs to, (2) what property makes it resist clean classification, and (3) whether the problem is the item or the boundary. If you can't find three misfits, your system is probably too coarse to be useful.

Common pitfall: Treating boundary cases as exceptions to ignore rather than evidence to examine. The instinct is to force the ambiguous item into the nearest category and move on — filing the tomato under 'vegetable' and forgetting about it. This preserves the illusion that your system is complete while guaranteeing it will fail silently whenever the next boundary case arrives. The opposite failure is equally dangerous: treating every boundary case as proof that categories are useless, and abandoning classification entirely.

This practice connects to Phase 12 (Classification and Typing) — building it as a repeatable habit compounds over time.