The Art of War by active 6th century B.C. Sunzi

22. When he utilises 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. [Ts’au Kung calls this "the use of natural or inherent power."]