Cognitive Biases Everyone Falls For

What is this page about?

A field guide to fifteen cognitive biases that predictably distort judgment, framed by Tversky and Kahneman's 1974 heuristics-and-biases work and the point that biases are the cost of processing information under constraints, not moral failures. It defines and illustrates confirmation bias, the sunk-cost fallacy, Dunning-Kruger, the availability heuristic, anchoring, hindsight bias, survivorship bias, the fundamental attribution error, the halo effect, loss aversion, framing, recency bias, the planning fallacy, ingroup bias, and optimism bias, and stresses building countermeasures rather than trying to eliminate them.

What has been corrected on this page?

Every accepted correction to this page is recorded with the exact change, so readers can see how the page improved over time.

1. 11 July 2026 · corrected by Emir Baycan

   Flyvbjerg, Holm & Buhl found mean road cost overruns of ~20%, not 28%; rail (~45%) and bridges/tunnels (~34%) are correct.

   Before

   mean overruns of 28 percent for roads, 45 percent for rail, and 34 percent for bridges

   After

   mean overruns of 20 percent for roads, 45 percent for rail, and 34 percent for bridges

   Why: Body content was already correctly fixed on the live site. Found and fixed an independent, differently-worded fabrication in the FAQ: 'mean overruns of 28 to 45 percent depending on project type' still preserved the unverified 28% figure, corrected to the body's exact per-category breakdown (20% roads / 45% rail / 34% bridges), re-encoded via the standard 4-step faq op-sequence (base64,json,base64,json), round-trip verified before and after PUT, confirmed clean on live re-fetch.

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1 contributor has checked "Cognitive Biases Everyone Falls For" on When Notes Fly. Each name below links to that person's public CitePep profile, where every contribution they have made is listed with the exact change they proposed.