Tesler's Law of the Conservation of Complexity

Larry Tesler, one time vice president of Apple argued that the total complexity of a system is a constant - - as you make the person's interaction simpler, the hidden complexity behind the scenes increases.  Make one part of the system simpler, said Tesler, and the rest of the system gets more complex.  Trade-off - - making things easier for the user means making it more difficult for the designer or engineer.