Following up on yesterday's post, I invite you to look at the logo to the right. Undoubtedly, it is one you have seen hundreds, if not thousands, of times. How many of you, however, have ever noticed the arrow between the "E" and "x." It is a wonderful example of negative space and I want you to think of it as a metaphor for training your mind to "see what isn't there."
Naturally, this led RAF officials to recommend that those areas of the plane be reinforced with extra armor. Wald, however, reached just the opposite conclusion. He argued that data was only being collected from the planes that had successfully completed their mission. It didn’t include those unlucky enough to be shot down in battle. Recognizing that this created a selection bias, Wald came to the counterintuitive conclusion that the parts of the returning planes that were not riddled with holes should be the areas that received additional fortification. Why? Because he understood that those areas of the aircraft that had been hit and yet still made it back were not critical to the mission’s success.
Wald was only able to do this by "seeing what wasn't there." He "saw" the aircraft that didn't return.