The art of war

One who knows the enemy and
knows himself will not
fear the result of a hundred battles.

One who does know himself
but not the enemy will
sometimes win and sometimes suffer a defeat.

One who does know neither
the enemy nor himself will be in
danger in every battle.

Knowing the enemy
enables you to take the offensive,
knowing yourself
enables you to stand on the defensive."

- Sun Tzu 'The art of war'