"We recognize that there will be User's Models and that the sum total of all the astute User's Models will be approximately equivalent to the Designer's Model, if [the designer] has done a good job of representing that model in the embodiment of the system."

"Design is always hard. There is always something that you never thought of which manifests itself at the end of the process and proves to be the most challenging. As a result, you must adopt a process which expects the unexpected and is flexible to change.

Waterfall methodology is definitely out. Iterative methods are essential."