This is a Lexicon entry: the mechanism, when it shows up, and the countermeasure. The full correction, with real-world cases and the audit prompt, hasn't been written yet.
Definition
The well-documented tendency for people to be more confident in their answers, predictions and judgments than their accuracy warrants. When people say they are "99% certain," research suggests they are wrong roughly 40% of the time (Fischhoff, Slovic & Lichtenstein, 1977).
When it shows up
Making predictions; expressing certainty; in any context where you are asked to assign a probability. Modern context: A team asked to give 90% confidence intervals for project delivery dates produces intervals that contain the actual date 45% of the time. After being shown this data, they produce intervals that contain the actual date 50% of the time. The correction is real but insufficient. High-stakes instance: Venture investment - the majority of professional venture capital funds underperform public market indices net of fees, despite managers' consistent confidence in above-average performance at time of fund raise. Failure mode: Making worse bets, taking on too much risk, under-preparing for bad outcomes. "I'm 99% sure" when you should be 60% sure. Estimated cost: High - often irreversible where this bias dominates unchecked decisions.
Failure mode
Making worse bets, taking on too much risk, under-preparing for bad outcomes. "I'm 99% sure" when you should be 60% sure.
Countermeasure
Track your predictions. Use calibration training exercises. Practice expressing beliefs as probability ranges rather than certainties. Ask: "What's the chance I'm wrong?" When correction costs more than the bias: For execution: modest overconfidence about one's own ability improves performance on difficult tasks by sustaining motivation and reducing decision paralysis. The correction is most important for prediction and forecasting tasks. For motivation and execution, calibrated confidence is often better than accurate confidence.
Related traps
Also connected in the mapThe Bias Blind Spot·15 more, locked
Credit & first seen
DiscoveredLichtenstein, S.&Fischhoff, B. (1977).'Do those who know more also know more about how much they know?'Organisational Behaviour and Human Performance 20(2), 159-183 source ↗
Read next
Entry #40 of 631 in The Lexicon · see the full Lexicon