Simplification is as much in the mind as it is in the device.

Learning should take place when it is needed, when the learner is interested, not according to some arbitrary, fixed schedule

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

So what does a good teacher do? Create tension - but just the right amount.

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.

When a device as simple as a door has to come with an instruction manual—even a one-word manual—then it is a failure, poorly designed.

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