Complexity is acceptable as long as it is intelligible and necessary. We want to avoid needless complications.

Readers always seem to think that the author has some control over the design of their books.

Design is really an act of communication, which means having a deep understanding of the person with whom the designer is communicating.

Also note that invariably when we design something that can be used by those with disabilities, we often make it better for everyone

Isn't one of your first exercises in learning how to communicate to write a description of how to tie your shoelaces? The point being that it's basically impossible to use text to show that

It is relatively easy to design for the perfect cases, when everything goes right, or when all the information required is available in proper format

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.