Henry Ford Sr. (1863 – 1947)

“… 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.”

Or more succinctly …

K’naan (Keinan Abdi Warsame) (1978 – )

“… any man who knows a thing, knows he knows not a damn, damn thing at all …”