The first post in the Mental Models for Corporate Counsel series.
The story goes as follows: In World War II, some very smart designer was asked to imagine a better bomber for the Air Force. The Air Force presented him with their research, including photographs of bombers that had returned from air raids over Germany. The photos showed damage caused by German anti-aircraft defences, and the Air Force told the smart designer that any aircraft she came up with would need additional armour in those spots - because clearly that’s where the aircraft often get hit.
The smart designer saw through the survivorship bias, though. There was no need for extra armour in those spots, she told them, because the photographs proved that aircraft could be shot in those areas and still make it home safely. It was those parts without any damage that needed the extra armour - none of the aircraft that were damaged in those parts made it home at all.
The Air Force was using ‘returned aircraft’ as their sample group, when really they should have used ‘departing aircraft’.