Not Random Errors — Predictable Ones
A cognitive bias is a systematic pattern of deviation from rational judgment. Unlike random mistakes, biases are predictable: the same type of person, facing the same type of situation, tends to err in the same direction. This predictability is what makes the study of cognitive biases so valuable — and so actionable.
The field was shaped decisively by the collaboration between Israeli psychologists Daniel Kahneman and Amos Tversky, who began working together at the Hebrew University of Jerusalem in the late 1960s. Their 1974 paper in Science, "Judgment Under Uncertainty: Heuristics and Biases," introduced the idea that people rely on a small number of mental shortcuts — heuristics — when making judgments, and that these shortcuts produce systematic, predictable errors.
Their 1979 paper, "Prospect Theory: An Analysis of Decision Under Risk," directly challenged the dominant economic model of rational choice. It became one of the most cited papers in economics, and eventually led to Kahneman receiving the Nobel Prize in Economics in 2002. (Tversky had died in 1996; the prize is not awarded posthumously.)
Heuristics vs Biases
It is important to distinguish between heuristics and biases. A heuristic is a mental shortcut — a fast, efficient rule of thumb that helps us navigate complex decisions without exhaustive analysis. Most of the time, heuristics work well enough. The problem arises when they are applied in contexts where they systematically lead us astray. That systematic misapplication is a bias.
Think of it this way: using a compass to navigate is a heuristic that works well in most terrain. But near magnetic anomalies, following the compass leads you wrong every time. The compass hasn't changed — the environment has created conditions where the heuristic fails reliably.
The Scope of the Problem
Since Kahneman and Tversky's foundational work, researchers have catalogued hundreds of distinct cognitive biases. A 2016 effort by writer Buster Benson and designer John Manoogian III organised these into a visual "cognitive bias codex," grouping roughly 188 named biases into four broad categories based on the problem they arise from: too much information, not enough meaning, the need to act fast, and the limits of memory.
This breadth matters. Cognitive biases are not a niche quirk of psychology — they permeate every domain of human judgment, from medicine and law to investing and everyday spending.
Why This Matters for Financial Decisions
Financial decisions are particularly vulnerable to cognitive bias because they involve exactly the conditions under which heuristics fail: uncertain outcomes, numerical estimates, emotional stakes, and social influence. The combination of Kahneman and Tversky's foundational research with later work in behavioural economics and finance has produced a detailed map of where human financial judgment tends to go wrong — and why.
Understanding what a cognitive bias is, and that they arise from normal cognitive processes rather than stupidity or weakness, is the necessary first step. You cannot address what you have not named.