airplane rule

airplane rule n.  "Complexity increases the possibility of
   failure; a twin-engine airplane has twice as many engine problems
   as a single-engine airplane."  By analogy, in both software and
   electronics, the rule that simplicity increases robustness.  It is
   correspondingly argued that the right way to build reliable systems
   is to put all your eggs in one basket, after making sure that
   you've built a really *good* basket.  See also {KISS
   Principle}.