In the chapter on weak points and strong points in The Art of War, Sunzi compares an army to water. “Water shapes its flow according to the ground. An army shapes its victory according to the enemy.” (水因地而制流，兵因敵而制勝)
He goes on: “So an army has no constant formation, and water has no constant shape. One who can win by changing with the enemy is called divine.” (故兵無常勢，水無常形。能因敵變化而取勝者，謂之神。)