A good designer will actually design the company.
The hardest part of design ... is keeping features out.
The designer has an obligation to provide an appropriate conceptual model for the way that the device works. It doesn't have to completely accurate but it has to be sufficiently accurate that it will help in both the learning of the operation and also dealing with novel situations.
I prefer design by experts - by people who know what they are doing
Knowing how people will use something is essential
Readers always seem to think that the author has some control over the design of their books.