The golden rule of systems design is this,

* create a few simple principles which every component obeys at all times

the first lemma to the golden rule is

* never violate the golden rule

the second lemma to the golden rule is

* don't make exceptions

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Some of the consequences of the golden rule are that if a feature deviates from the principles in the system then it shouldn't exist. It should be removed or preferably not ever added. Also, the system should be optimized for the general case. If you ever find yourself writing code "in case" some user wants it, delete it immediately.

Applying the golden rule prevents the onset of CreepingFeaturitis.