None of our men are "experts."  We have most unfortunately found it necessary
to get rid of a man as soon as he thinks himself an expert -- because no one 
ever considers himself expert if he really knows his job.  A man who knows a 
job sees so much more to be done than he has done, that he is always pressing 
forward and never gives up an instant of thought to how good and how efficient 
he is.  Thinking always ahead, thinking always of trying to do more, brings a 
state of mind in which nothing is impossible. The moment one gets into the
"expert" state of mind a great number of things become impossible.
		-- From Henry Ford Sr., "My Life and Work"