The system should treat all user input as sacred.
As far as the customer is concerned, the interface is the product.
Right now, computers, which are supposed to be our servant, are oppressing us.
A computer shall not harm your work or, through inaction, allow your work to come to harm.
Users do not care about what is inside the box, as long as the box does what they need done.
An interface is humane if it is responsive to human needs and considerate of human frailties.
A computer shall not waste your time or require you to do more work than is strictly necessary.
Once the product's task is known, design the interface first; then implement to the interface design.
Imagine if every Thursday your shoes exploded if you tied them the usual way. This happens to us all the time with computers, and nobody thinks of complaining.