Focus on the human, not the machine
The shift in thinking required to fix that error - from focusing on the machine to focusing on the human using it - was the first step down the path that led to the iPhone and the iPad today.
Pilot error?
By the end of the war, there had been thousands of such crashes. They were generally attributed to pilot error - after all, wartime had necessitated quickly training a lot of new pilots.
Psychologists to the rescue
The accidents remained a mystery until after the war, when psychologists Paul Fitts and Alphonse Chapanis finally figured it out - and the answer was stupidly simple.
Identical controls, opposite functions
The control that lowered the landing gear and the one that lowered the wing flaps looked identical. It was all too easy for a pilot, especially at night, to reach for the landing gear control and grab the wing flap one instead.
Shape coding
Chapanis pioneered the field of shape coding by creating a system of levers and knobs for airplanes in which each control had a different shape, making it much harder to mistake any of them for something else. He’s considered one of the creators of the field of ergonomics.
Design for human behavior
B-17 redesign was the first time it occurred to anyone that we should design machines to accommodate human behavior instead of retraining human behavior to fit machines.