So a military force has no constant formation, water has no constant shape: the ability to gain victory by changing and adapting according to the opponent is called genius.
When he utilizes combined energy, his fighting men become as it were like unto rolling logs or stones. For it is the nature of a log or stone to remain motionless on level ground, and to move when on a slope; if four-cornered, to come to a standstill, but if round-shaped to go rolling down.
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.
One whose troops repeatedly congregate in small groups here and there, whispering together, has lost the masses. One who frequently grants rewards is in deep distress. One who frequently imposes punishments is in great difficulty. One who is at first excessively brutal and then fears the masses is the pinnacle of stupidity.
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.
Therefore the skillful leader subdues the enemy's troops without any fighting; he captures their cities without laying siege to them; he overthrows their kingdom without lengthy operations in the field.