From the Tang-era frontier tradition; most commonly attributed to
高适 (Gao Shi) in his 《
自淇涉黄河途中作》 or similar Tang five-character verse extolling martial spirit:
昔贤多使气,
忧国不谋身 (The worthies of old were given to temper — they worried about the state and took no thought for themselves).
使气 = to let one's
气 (spirit / temper) have its way — refusing meekness when principle demands. A staple Tang-Song political-moral idiom.