The Planes That Came Back

During World War II, the military examined bombers returning from missions and found bullet holes concentrated on the wings and fuselage. The plan was to add armor there. Statistician Abraham Wald said the opposite: armor the places with no bullet holes. Why?

This is survivorship bias — drawing conclusions only from the things that survived a selection process while ignoring those that did not. The military was studying survivors and assuming they represented every case. The missing planes told the real story.