Great Software is like a well made power tool

  1> easy to understand
  2> reliably does what you expect
  3> works well with the compute power you have available, doesn't waste it
  4> works well with accessories, in a predictable manner
  5> can be applied in a wide range of situations, without breaking above

Great operating systems are like using an electrical outlet

  1> Easy to understand
  2> Supplies only the resource you expect, and nothing else
  3> Stops the load if it tries to gobble up resources
  4> Doesn't let the load send things elsewhere(like a ground fault detector)