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11.5 — The Biases That Actually Cost You
There are lists of two hundred cognitive biases. They are useless — nobody can hold two hundred things in mind, and many are the same effect under different names.
This page has twelve. They are the ones that cost real money, real time and real relationships, and each comes with the specific check that catches it.
They all come from the same source (2.5): a heuristic that is right most of the time, applied to a case it was not built for.
The ones that cost you money
Sunk cost
Continuing because of what you have already spent.
The finished project nobody wants. The relationship kept going because of the years in it. The share held because you paid more than it is worth. The course finished because it was expensive.
Why it is wrong: the money and time are gone in every possible future. Only the remaining costs and benefits can differ between your options, so the past investment is not a reason.
The check: if I were arriving at this situation today, with no history, would I choose to continue? If no, the only thing holding you is the sunk cost.
Loss aversion
Losses feel considerably worse than equivalent gains feel good. The commonly cited ratio is around two to one, though the size is debated and the phenomenon is well replicated.
What it produces: holding losing positions too long, refusing sensible risks, being far more upset about a small loss than pleased about a large gain, and being manipulated by anything framed as a loss.
The check: restate the decision in terms of final position rather than change. Not "I'll lose ₹40,000" but "I'll have ₹3,60,000 rather than ₹4,00,000, and here is what each buys me."
Anchoring
The first number mentioned shapes every subsequent judgement, even when it is obviously irrelevant.
The check: decide your number before you hear theirs, and write it down. This is the single most valuable habit in any negotiation (17.12).
The endowment effect
You value something more once it is yours. Sellers consistently price at more than buyers will pay for the identical item.
The check: what would I pay for this today if I did not own it? That is what it is worth.
The ones that cost you time and decisions
Planning fallacy
Almost everything takes longer than you estimate, and the effect persists even for people who know about it and have been late on every previous occasion.
Why: you estimate from the specifics of this case — the inside view (1.8) — and the specifics never include the interruptions, the illness and the thing nobody thought of.
The check: the outside view. How long did the last five things like this actually take? Then use that number, and resist the urge to explain why this one is different.
Availability
You judge likelihood by how easily an example comes to mind (2.5), which tracks how memorable something is rather than how common.
What it costs: fear of the vivid and rare, complacency about the boring and common. Also, in relationships: your sense of a person is dominated by the last three interactions, not by the average of two hundred.
The check: ask for the base rate. How often does this actually happen, per hundred cases?
Confirmation bias
Covered in 1.4 and it belongs on any list of the expensive ones. You seek and weight evidence that supports what you already think.
The check: what would change my mind, and have I looked for it?
Hindsight
Once you know the outcome, it feels as though it was predictable, and you misremember having expected it.
What it costs: unfair judgement of other people's decisions, unfair judgement of your own, and — worst — it prevents learning, because if the outcome was obvious there is nothing to learn.
The check: written predictions, dated, before the outcome (1.4). It is the only defence, because your memory of what you thought is unreliable.
The ones that cost you relationships
Fundamental attribution error
Their behaviour is their character; yours is your circumstances (5.8, 10.5). The most expensive bias in this list, in terms of damage done.
The check: what situation would make a reasonable person do this?
Self-serving bias
Success is mine, failure is circumstances. Universal, and it operates in groups too — which is why every department believes it does more than its share and is more reasonable than the others.
And it produces a specific measurable effect: ask both members of a couple what percentage of the housework they do, and the two figures reliably total well over a hundred. Not because either is lying — each remembers their own contributions better (2.4).
The check: before claiming credit or assigning blame, ask what the other side would say. And in the housework case: assume the true figure is closer to the middle than your estimate.
Naive realism
The belief that you see things as they are, and that people who disagree are biased, misinformed or dishonest.
The specific and well-documented version: people rate themselves as less biased than others, and this holds even when the bias is explained to them first.
What it costs: every political and family argument you have ever had.
The check: what would a reasonable, informed, well-intentioned person who disagrees with me believe, and why? If you cannot produce it (1.8), you are in naive realism.
The false consensus effect
You overestimate how many people agree with you. Your sample is people like you (1.5), and you fill in the rest from yourself.
The check: ask, rather than assuming. And treat any sentence beginning "everyone thinks" as a report about your social circle.
Why knowing about them barely helps
The uncomfortable finding, and it needs saying because the whole genre of bias lists is built on ignoring it.
Simply knowing about a bias does not reliably reduce it. Studies of debiasing find that education alone produces little. The bias operates before you have a chance to apply your knowledge.
And there is a specific perverse effect: the bias blind spot. People who learn about biases become better at spotting them in other people and no better at spotting them in themselves. You will read this page and think of three colleagues.
What does work
Not knowledge. Procedures that do not depend on you noticing in the moment.
Write the estimate or prediction down first, before the anchor, before the outcome, before the discussion. This single habit defeats anchoring, hindsight and self-serving recall simultaneously (1.4).
Use the outside view for anything you are estimating.
Use a checklist for repeated decisions, so the check is mechanical.
Ask another person, specifically someone who will disagree. Their biases are different from yours, and — crucially — you can see theirs, and they can see yours.
Set rules with numbers in them in advance. Exit conditions, spending limits, deadlines. A rule made by a version of you with no stake beats a judgement made by a version with one (8.6).
And build in a delay for anything significant. Most of these biases are strongest in the moment.
What to do with this
Pick the one that has cost you most, honestly. Most people know which. Sunk cost and the attribution error are the two most common answers.
Write its check on something you will see — the wall, a card, the top of your notes.
Start the prediction diary. Dated, before the outcome, one line. It is the only defence against hindsight, and hindsight is what stops you learning from everything else.
And apply the relationship column first. The money biases cost you money and the relationship biases cost you people. The single highest-return item on this page is asking what situation would make a reasonable person behave as this person just did, and it takes four seconds.
Next: 11.6 covers the bias that operates at group scale rather than individual — how "us and them" forms, how little it takes, and what actually reduces it.