21. The clever combatant looks to the effect of com- bined energy, and does not require too much from indi- viduals. Hence his ability to pick out the right men and utilize combined energy. 22. 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 motion- less 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.