- Do not add new functionality unless you know of some real application that will require it. - It is as important to decide what a system is not as to decide

- Do not add new functionality unless you know of some real application that will require it. - It is as important to decide what a system is not as to decide what it is. Do not serve all the world's needs; rather, make the system extensible so that additional needs can be met in an upwardly compatible fashion. - The only thing worse than generalizing from one example is generalizing from no examples at all. - If a problem is not completely understood, it is probably best to provide no solution at all. - If you can get 90 percent of the desired effect for 10 percent of the work, use the simpler solution. (See also worse is better.) - Isolate complexity as much as possible. - Provide mechanism rather than policy. In particular, place user interface policy in the clients' hands.