This excerpt comes from Explanation Six in Han Feizi · Inner Congeries of Sayings I. Han Fei holds rulers should confront ministers with confirmed facts. Exposing one lie creates widespread fear of the ruler’s omniscience, restraining all hidden treacherous acts.
Han Feizi recounts Duke Huan sent a scout to watch rebellious Prince Jiu. The envoy spotted his unnatural forced smile and blank gaze, proving his plot. The duke pressured Lu to execute the prince, showing inner schemes reveal themselves via odd behaviors.