Falsifiability
Popper's test for whether an idea counts as knowledge: can you say what would prove it wrong? If nothing could ever refute your theory — if every piece of evidence somehow confirms it — then it's not science, it's a story you're attached to. Popper developed this by watching Freudians and Marxists explain away every counterexample. The most dangerous ideas aren't the ones that are wrong. They're the ones that can never be proven wrong.
Related ideas
Ideas connected to Falsifiability.
Overconfident ideas are often unfalsifiable — nothing could prove them wrong
Probabilistic ThinkingProbabilistic thinkers ask 'what would change the odds?' — a form of falsifiability
Inversion as a Thinking ToolBoth ask the same question from different angles: what would prove this wrong?
Intellectual HumilityIntellectual humility means being willing to say what would change your mind
Idols of the MindBacon diagnosed the disease; Popper provided the test — both fight self-deception