In warfare, there are no constant conditions. He who can modify his tactics in relation to his opponent will succeed and win.
One defends when his strength is inadequate, he attacks when it is abundant.
Attack him where he is unprepared, appear where you are not expected.
There are routes not to be followed, armies not to be attacked, citadels not to be besieged, territory not to be fought over.
He who knows his enemy and himself well will not be defeated easily.
If the enemy opens the door, you must race in.