Market segmentation s a natural result of the vast differences among people
Behavioral design is all about feeling in control. Includes: usability, understanding, but also the feel.
The designer shouldn't think of a simple dichotomy between errors and correct behavior; rather, the entire interaction should be treated as a cooperative endeavor between person and machine, one in which misconceptions can arise on either side.
Attractive things work better.
To me, error analysis is the sweet spot for improvement.
Readers always seem to think that the author has some control over the design of their books.