From 《
论语·
公冶长》(Analects, Gongye Chang, Confucius, c. 500 BCE). The backstory: Confucius first said
听其言而信其行 ('I used to listen to what people said and trust their actions'). But after catching his student Zai Yu napping during the day despite fine speeches, he changed his rule to
听其言而观其行 ('Now I listen to what they say AND watch what they do'). The proverb embodies Confucius's shift to empirical judgment.