How Not to Be Wrong · Jordan Ellenberg

You're only seeing the survivors

We draw lessons from the successes that are visible and forget the failures that were quietly removed from view. The missing data is often the most important data.

Survivorship bias: we learn from the winners we can see and miss the silent evidence of everything that didn't make it.

In WWII, the military wanted to armor bombers where returning planes showed the most bullet holes — the wings and fuselage. Statistician Abraham Wald argued the opposite: armor where the returning planes were untouched. The planes hit in the engines weren't in the data — they'd been shot down. The holes only showed where a plane could survive being hit.

That's survivorship bias: we draw conclusions from the successes that are visible and forget the failures that were quietly removed from view. "Study the habits of billionaires" ignores everyone who ran the same playbook and went broke. The losers don't write memoirs, so they vanish from the data.

Before copying a winner, ask: "Where are the people who did the same thing and failed — and would I even see them?" The absent cases are often the most informative ones. Look for the bullet holes that aren't there.

Why it matters

It's the single most common way smart people draw confident, backwards conclusions from incomplete data.

Test yourself

Where should you armor the plane — where returning bombers are hit, or where they aren't?
Show answer
Where they aren't hit. Planes hit there never came back — that's survivorship bias: the missing data matters most.

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Related ideas

Rare, unpredictable events shape history mostThe Black Swan→ Wealth is what you don't seeThe Psychology of Money→ Judge decisions by their quality, not their outcomeThinking in Bets→

FAQ

What is survivorship bias?
Survivorship bias is the error of drawing conclusions only from the people or things that survived a selection process, while ignoring those that didn't — and so never appear in the data. It produces overly optimistic, distorted conclusions.
What's the WWII airplane example of survivorship bias?
Statistician Abraham Wald advised armoring bombers where returning planes had no bullet holes, not where they did. Planes hit in those spots never made it back, so their absence — not the visible holes — revealed the vulnerable areas.