This is a picture tracking bullet holes on Allied planes that encountered anti-aircraft fire in WW2. At first, the military wanted to reinforce those areas, because obviously that’s where the ground crews observed the most damage on returning planes.
Until Hungarian-born Jewish mathematician Abraham Wald pointed out that this was the damage on the planes that made it home, and the Allies should armor the areas where there are no dots at all, because those are the places where the planes won’t survive when hit.
This phenomenon is called survivorship bias, a logic error where you focus on things that survived when you should really be looking at things that didn’t.
