Complexity means you have a large number of subcomponents and they interact in sometimes unexpected ways. Pilots don’t know, because they haven’t experienced the fringe conditions that are built into the system.
I was once in a room with five engineers who had been involved in building a particular airplane, and I started asking, ‘Well, how does this or that work?’ And they could not agree on the answers. So I was thinking, If these five engineers cannot agree, the poor pilot, if he ever encounters that particular situation . . . well, good luck.”