The author is not arguing for simplicity per se, but about being able to insert a human into a system that is normally automated. The example about the ship's steering system is perfect, actually. The system is not "simple" (if I were on a ship and the steering failed, I would be clueless), but it provides plenty of interjection points where a knowledgeable human can step in and either debug or fix the issue. It's th…
I think a key element is that this system is composed of parts that have one input. That allows a human to replace a component that failed and provide that single input to the next component in line.