In WWII, Allied planes would often return to their bases with hundreds of holes from enemy guns. This inspired crafty ground crews to bolt on metal plating over the holes to strengthen the planes and prevent future losses. They assumed that the evidence clearly indicated where they should place the extra protection.
But one American scientist wasn’t so sure… Abraham Wald, a brilliant mathematician and statistician, intervened and pointed out that while the surviving planes had been hit severely, they were still able to fly safely home.
He urged the military commanders to add more armor to the parts of the plane where there was NO DAMAGE. Wald theorized that the planes that didn’t make it back must have been hit in different places than the planes that did make it back.
In other words, it was the other parts of the plane that needed reinforcements – not the parts with obvious holes.
Enlightened commanders adopted Wald’s recommendation and his brilliant intervention would end up saving the lives of thousands of Allied airmen.
Survivorship Bias: A Universal Human Error
Wald’s mind-blowing theory about the bombers’ weak spots is a classic example of survivorship bias. This is actually a common human error that leads us to pay more attention to survivors and “winners” instead of trying to understand the failures.
Almost everyone has survivorship bias without realizing it. Our entire global culture is about celebrating winners and forgetting the losers.
As author David McRaney writes in his amazing article on Survivorship Bias: “If you are thinking about opening a restaurant because there are so many successful restaurants in your hometown, you are ignoring the fact that only successful restaurants survive to become examples. Maybe on average 90 percent of restaurants in your city fail in the first year. You can’t see all those failures because when they fail they also disappear from view.” As Nassim Taleb writes in his book The Black Swan, “The cemetery of failed restaurants is very silent.”
Think about these other examples of how you (and millions of others) focus solely on “survivors:”