Push the Button

Crash landed B-17 and Pilot Controls

From  The UX of LEGO Interface Panels by George Cave:

Differentiating inputs 

What could cause 400 WWII pilots to raise the landing gear on their B-17 bomber just before touchdown? Catastrophic pilot error, or something more fundamental? 

It was the psychologist Alphonsis Chapanis who first suggested that the high rate of crash landings might be the fault of poor interface design. The adjacent landing gear and flap control knobs were identically shaped. The pilots never stood a chance. 

His temporary solution was to glue differently shaped strips of rubber to each switch, enabling blind operation by touch alone. This gave rise to the idea of shape coding and a system of differentiation still being followed in aircraft cockpits today.

 Via David Malki