The art of using troops is this:
......When ten to the enemy's one, surround him;
......When five times his strength, attack him;
......If double his strength, divide him;
......If equally matched you may engage him;
......If weaker numerically, be capable of withdrawing;
......And if in all respects unequal, be capable of eluding him,
..........for a small force is but booty for one more powerful.
Whoever is first in the field and awaits the coming of the enemy, will be fresh for the fight; whoever is second in the field and has to hasten to battle will arrive exhausted.
If an enemy has alliances, the problem is grave and the enemy's position strong; if he has no alliances, the problem is minor and the enemy's position weak.
Hence the saying: If you know the enemy and you know yourself, your victory will not stand in doubt; if you now Heaven and you know Earth, you may make your victory complete.