No True Scotsman

An informal logical fallacy where counterexamples are dismissed by retroactively redefining the category to exclude them. 'No true entrepreneur would fail at that'—and when one does, they're reclassified as 'not a real entrepreneur.' The fallacy makes beliefs unfalsifiable by turning definitions circular: the category is defined by the conclusion, making disconfirmation impossible. It's the enemy of learning from failure.

When to use it

When evaluating arguments that seem immune to counterexamples; when post-hoc reclassification is used to explain away failures; when definitions shift to protect conclusions; during debates where terms keep getting redefined as inconvenient evidence appears.

How it can help

Detects when you or others are protecting beliefs from disconfirmation. Watch for it in post-mortems ('that wasn't a real test of the strategy'), hiring ('a real A-player wouldn't have struggled'), and ideology ('a true [X] would never [Y]'). The antidote is fixing definitions BEFORE seeing results. If you can't specify in advance what would disprove your belief, you may be in No True Scotsman territory.