Confucius said: “There are three tendencies that a leader should guard against. When he is young and his blood and spirit are still unstable he should guard against lust. When he is in the prime of life and his blood and spirit have reached their full strength, he should guard against aggressiveness. When he is old and his blood and spirit have weakened, he should guard against greed.”
A very perceptive description of the three main stages that men go through in life: the secret to becoming a “leader” is to learn to control your natural masculine instincts.
I was tempted to translate 氣 (qì) as “hormones”, at least when describing the condition of a man when he is young but for the sake of consistency decided to stick to “spirit”. 血 (xuè) could also be rendered as “body” rather than “blood”.