I still think of this one whenever some lab apparatus starts working after an expert walks in and fiddles with some wires or power-cycles it --

  A novice was trying to fix a broken lisp machine by turning the power off and on.  
  Knight, seeing what the student was doing, spoke sternly - 
  "You can not fix a machine by just power-cycling it with no understanding 
  of what is going wrong."
  Knight turned the machine off and on.
  The machine worked.