Survivorship Bias
The Psychology Behind It
History is written by the victors. In data, history is written by the survivors. When we look for patterns, we naturally look at the visible data. But often, the most important data is the data that is missing.
The most famous example comes from WWII. The military looked at planes returning from battle to see where they had been shot, planning to reinforce those areas. Statistician Abraham Wald stopped them. He pointed out that they were only looking at the planes that survived. The planes that were hit in the engines or cockpit didn't come back. Therefore, the bullet holes on the returning planes showed where a plane could be hit and still survive. They needed to reinforce the areas with no bullet holes.
Real-World Examples
Business Advice
We study successful companies (Apple, Google) and try to copy their habits. "Steve Jobs dropped out of college, so I should too!" We ignore the thousands of dropouts who started failed companies. Their stories are not on the magazine covers.
Architecture
"They don't build them like they used to." We look at old buildings and think they were built better. In reality, the badly built old buildings collapsed or were demolished long ago. Only the strong ones survived.
Music
"Music from the 70s was so much better." We only listen to the hits that stood the test of time. We have forgotten the 99% of terrible songs that were on the radio back then.
Consequences
Survivorship bias can lead to:
- False Causality: We attribute success to random traits (e.g., "waking up at 4 AM") rather than the actual factors.
- Overconfidence: We underestimate the difficulty of success because we don't see the failures.
- Risky Behavior: We take risks (like skipping insurance) because "I've never had an accident before" (survivor logic).
How to Mitigate It
Look for the graveyard.
- Ask "What is missing?": When presented with data, ask what data was excluded or destroyed.
- Study Failure: Don't just read biographies of billionaires. Read post-mortems of failed startups. They often did the exact same things as the winners, but had bad timing or bad luck.
- The Base Rate: Always ask for the success rate of the entire pool, not just the characteristics of the winners.
Conclusion
Survivorship bias is the invisible silent killer of truth. It tricks us into believing that success is easy and predictable. By remembering the silent majority of failures, we can see the world—and the odds—more clearly.