Donald Norman — American Scientist

Donald Arthur "Don" Norman is the director of The Design Lab at University of California, San Diego... (wikipedia)

So what does a good teacher do? Create tension - but just the right amount.
In my opinion, no single design is apt to be optimal for everyone.
To me, error analysis is the sweet spot for improvement.
We expert teachers know that motivation and emotional impact are what matter.
I prefer design by experts - by people who know what they are doing.