Destructive selection bias

Whilst doing some research for some distribution curves I came across the work of Abraham Wald

Wald noted that the study only considered the aircraft that had survived their missions—the bombers that had been shot down were not present for the damage assessment. The holes in the returning aircraft, then, represented areas where a bomber could take damage and still return home safely. Wald proposed that the Navy instead reinforce the areas where the returning aircraft were unscathed, since those were the areas that, if hit, would cause the plane to be lost. This is still considered today seminal work in the then-fledgling discipline of operational research.