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

43. Therefore soldiers must be treated in the first instance with

humanity, but kept under control by means of iron discipline. [Yen Tzŭ [B.C. 493] said of Ssu-ma Jang-chu: "His civil virtues endeared him to the people; his martial prowess kept his enemies in awe." Cf. Wu Tzŭ, ch. 4 init.: "The ideal commander unites culture with a warlike temper; the profession of arms requires a combination of hardness and tenderness."] This is a certain road to victory.