Foreknowledge cannot be gotten from ghosts and spirits, cannot be had by analogy, cannot be found out by calculation. It must be obtained from people, people who know the conditions of the enemy.
If ignorant both of your enemy and yourself, you are certain to be in peril.
He who knows when he can fight and when he cannot, will be victorious.
There has never been a protracted war from which a country has benefited.
If you are far from the enemy, make him believe you are near.
He who is prudent and lies in wait for an enemy who is not, will be victorious.