Logical Fallacies
A logical fallacy is a flaw in reasoning that makes an argument invalid or misleading — even when the conclusion happens to be true. Fallacies exploit the gap between how the brain actually processes information (fast, pattern-matching, narrative-driven) and how it should reason (slow, evidence-weighted, probabilistic).
This page collects every logical fallacy and cognitive bias in the Faster Than Normal mental models library. Each card links to a full breakdown with definitions, real-world examples, and practical advice on when the fallacy helps (yes, some do) and when it misleads.
Use this as a reference during decisions, debates, pitch reviews, or investment analysis. Spotting fallacies in your own thinking is harder than spotting them in others — but far more valuable.
All fallacies & biases (33)
Confirmation Bias
We seek evidence that confirms what we already believe and filter out what contradicts it.
Psychology & BehaviorSurvivorship Bias
Abraham Wald
Studying only survivors produces systematically wrong conclusions.
Psychology & BehaviorSunk Cost Fallacy
Alfred Marshall
Past investments should not drive future decisions.
Psychology & BehaviorNarrative Fallacy
Nassim Nicholas Taleb
We compress complex reality into clean stories, mistaking explanation for prediction.
Psychology & BehaviorGambler's Fallacy
On August 18, 1913, at the Monte Carlo Casino, the roulette wheel landed on black. Then black again. And again. Twenty-six consecutive times. Gamblers watched the first ten spins...
Psychology & BehaviorPlanning Fallacy
Kahneman / Tversky
People systematically underestimate time, cost, and risk of projects.
Psychology & BehaviorFundamental Attribution Error
Lee Ross
We blame character when circumstances are the real cause.
Psychology & BehaviorDunning-Kruger Effect
David Dunning & Justin Kruger
Low competence breeds overconfidence; expertise breeds doubt.
Psychology & BehaviorAnchoring
Kahneman & Tversky
First information encountered disproportionately shapes all subsequent judgements.
Psychology & BehaviorFraming Effect
Tversky & Kahneman
How you frame the question determines the answer you get.
Psychology & BehaviorHalo Effect
Edward Thorndike
One positive trait colours evaluation of everything else.
Psychology & BehaviorBandwagon Effect
People adopt trends because others have — popularity self-reinforces.
Psychology & BehaviorHindsight Bias
Baruch Fischhoff
After the fact, people believe they knew it all along.
Psychology & BehaviorAvailability Cascade
Timur Kuran / Cass Sunstein
In 1999, Timur Kuran and Cass Sunstein published a paper that explains half of what goes wrong in public discourse: "Availability Cascades and Risk Regulation." The concept is a...
Psychology & BehaviorLoss Aversion
Kahneman & Tversky
Losses hurt roughly twice as much as equivalent gains feel good.
Psychology & BehaviorStatus Quo Bias
William Samuelson / Richard Zeckhauser
Loss aversion applied to change makes inaction the default choice.
Mathematics & ProbabilityScope Neglect
Paul Slovic
Scope neglect is the failure to adjust judgment or willingness to pay when the scale of the problem changes. People often react similarly to "100 birds at risk" and "10,000 birds...
Psychology & BehaviorLudic Fallacy
Nassim Nicholas Taleb
The Ludic Fallacy — from the Latin ludus, meaning game — is the mistake of applying the clean, well-defined rules of games and models to the messy, open-ended reality of the real...
Psychology & BehaviorAnecdotal Fallacy
The anecdotal fallacy is using a personal experience or single example as proof of a general claim — substituting a vivid story for statistical evidence. "My uncle smoked his...
Psychology & BehaviorIllusion of Control
Ellen Langer
In 1975, Ellen Langer ran a deceptively simple experiment at Yale. She sold lottery tickets to office workers. Half chose their own ticket. Half were assigned one at random....
Psychology & BehaviorNormalcy Bias
Normalcy Bias is the tendency to assume that because something has never happened before, it won't happen — or that because things have always been a certain way, they'll continue...
Psychology & BehaviorOptimism Bias
Optimism Bias is the tendency to overestimate the likelihood of positive outcomes and underestimate the likelihood of negative ones — particularly for events involving yourself....
Psychology & BehaviorNegativity Bias
Negativity Bias is the tendency for negative experiences, information, and emotions to have a disproportionately larger effect on psychological states and decisions than neutral...
Psychology & BehaviorEndowment Effect
Thaler / Kahneman / Knetsch
Ownership inflates perceived worth beyond objective value.
Psychology & BehaviorNeglect of Probability
Kahneman & Tversky / Gerd Gigerenzer
Humans don't evaluate risk by computing probabilities. They evaluate risk by imagining outcomes. The more vivid the outcome — the more easily they can picture the plane crash, the...
Psychology & BehaviorOutcome Bias
Outcome Bias is the tendency to judge the quality of a decision based on its outcome rather than the quality of the decision-making process at the time it was made. A risky bet...
Psychology & BehaviorSelf-Serving Bias
Self-Serving Bias is the tendency to attribute your successes to internal factors — talent, effort, intelligence — while blaming your failures on external circumstances — bad...
Psychology & BehaviorIngroup Bias
Ingroup Bias is the automatic tendency to favour members of your own group — giving them more trust, more benefit of the doubt, more resources, and more favourable interpretations...
Psychology & BehaviorAuthority Bias
Authority bias is the tendency to overweight the views or orders of people we see as authorities — titles, credentials, status — and to underweight the content of what they say....
Psychology & BehaviorAmbiguity Bias
Ambiguity bias is the tendency to prefer options where the probability of a favorable outcome is known over options where the probability is unknown — even when the unknown option...
Psychology & BehaviorOmission Bias
Omission Bias is the tendency to judge harmful actions as worse than equally harmful inactions — to feel that doing something that causes damage is morally and psychologically...
Psychology & BehaviorRecency Illusion
The Recency Illusion is the belief that something you've only recently noticed must itself be recent. You learn a new word and suddenly hear it everywhere; you discover a business...
Psychology & BehaviorZero-sum Heuristic
The zero-sum heuristic is the default cognitive shortcut that treats most interactions as zero-sum — where one party's gain must come at another's expense — even when the...
How to use this list
Before a major decision: scan the list for fallacies that apply to your situation. Confirmation bias and sunk cost fallacy are almost always relevant. Anchoring matters whenever numbers are involved.
During a debate: naming a fallacy is not an argument by itself — it is an invitation to examine the reasoning more carefully. “That sounds like survivorship bias — can we look at the failures too?” is more productive than “that’s a fallacy.”
For teams and organisations: build fallacy awareness into decision processes. Pre-mortems surface planning fallacy. Red teams catch confirmation bias. Structured estimation reduces anchoring. The fallacy is the diagnosis; the process change is the treatment.
Frequently Asked Questions
- What is a logical fallacy?
- A logical fallacy is a flaw in reasoning that undermines the logic of an argument. Fallacies can be formal (structural errors in deduction) or informal (errors in content, context, or relevance). They often feel persuasive because they exploit cognitive shortcuts — biases and heuristics — that the brain uses to process information quickly.
- What are the most common logical fallacies?
- The most frequently encountered logical fallacies include confirmation bias (seeking evidence that supports existing beliefs), sunk cost fallacy (continuing a losing course because of past investment), survivorship bias (drawing conclusions from winners while ignoring failures), the gambler's fallacy (believing past random events affect future probabilities), and anchoring (over-relying on the first piece of information encountered).
- How do logical fallacies differ from cognitive biases?
- Cognitive biases are systematic patterns in how the brain processes information — they are psychological tendencies. Logical fallacies are errors in reasoning or argumentation. In practice, many cognitive biases produce logical fallacies: confirmation bias (a cognitive tendency) leads to cherry-picking evidence (a reasoning error). This page covers both because understanding the bias helps you spot the fallacy.
- Why should I learn about logical fallacies?
- Recognising logical fallacies improves decision-making in business, investing, relationships, and everyday life. Founders avoid sunk cost traps, investors resist narrative fallacies, and leaders catch groupthink before it becomes strategy. Fallacy awareness is a core skill in critical thinking.
- Can logical fallacies be used intentionally?
- Yes — in rhetoric, marketing, politics, and negotiation, fallacies are often deployed deliberately. Anchoring is used in pricing, framing effects shape policy debates, and bandwagon appeals drive social proof campaigns. Understanding fallacies helps you both avoid being manipulated and communicate more honestly.