Find Out What You Don't Know by What You Do

Said in 1852 by the Duke of Wellington:

All the business of war, and indeed all the business of life,
is to endeavour to find out what you don't know by what you do;
that's what I called "guessing what was at the other side of the hill."

(cf Excremental Typo (2004-09-03), Mantra - Give More Praise (2019-07-28), ...) - ^z - 2020-03-13