The air was a major battlefield in World War II. At the height of war, the chance of a bomber aircraft crew returning home safely after a mission was only around 50%.

Abraham Wald, a renowned statistician and a member of the Applied Mathematics Panel in the United States, was assigned the task to increase aircraft survivability.

To avoid being shot down during a mission, the aircrafts needed more armour. The question was where to add the armour to?

Researchers looked at all the aircrafts that returned home safely, recorded where the bullet holes were, and recommended that armour be added to the areas that showed the most damage, on the ground that reinforcement should be added to areas that were mostly fiercely attacked.

Those who didn’t survive give us an equally important lesson as those who did.

Abraham Wald noticed that the study only looked at aircrafts that had survived their missions. That meant the bullet holes in the returning aircraft, counterintuitive it might seem, represented areas where a bomber could take damage and still return home.

Wald instead proposed that armour be reinforced to areas where the returning aircraft were unscathed, since those were the areas that, if hit, could cause fatal damage to the aircraft.

It is easy to get hung up on one side of the story. There are countless studies that look at what the successful have in common. But keep in mind that those who didn’t survive give us an equally important lesson as those who did.

What doesn’t work is as important as what does.