During the Spring and Autumn period, one evening, Duke Ling of Wei was sitting in his palace chatting with his wife when they suddenly heard the sound of a carriage approaching from the east. The noise stopped right at the palace gate, then, after a moment, resumed as the carriage headed westward. The Duke asked, "Who do you suppose that was?" His wife replied, "It must be Qu Boyu." Puzzled, the Duke pressed, "How can you be so sure?" She explained, "A true minister of great integrity, when passing the palace gate, will dismount out of respect, letting the carriage roll silently past. Qu Boyu is known for his unwavering propriety—he would never pass the ruler's gate without showing deference, even in the dark of night." The Duke sent a servant to investigate, and indeed, it was Qu Boyu. This story illustrates how keen observation of small actions can reveal a person's true character, a principle still valued in Chinese wisdom today.
Duke Ling of Wei asked Nanzi, "What is this all about?" "It is a carriage passing outside the palace; the person riding in it is likely the grand master Qu Boyu," Nanzi replied. "Why do you suspect it is Qu Boyu?" Duke Ling of Wei asked.
Nanzi replied, 'I have heard that all subjects must dismount to pay respects when passing the palace gate. A loyal minister and filial son is consistent in both public and private—never seeking applause in crowds nor acting dishonorably in solitude. Qu Boyu is a worthy minister of our state, most observant of rites. When his carriage passes the palace gate, he always dismounts to pay respects, and only after passing does he drive on. That is why I guessed it was him.'
Duke Ling of Wei, wanting to verify Nanzi's words, sent someone to investigate. The one who passed the palace gate was indeed Qu Boyu. But he deceived Nanzi, saying, "I sent someone to investigate. A carriage did pass the palace gate just now, but that person was not Qu Boyu. You guessed wrong."
Nanzi heard this and congratulated Duke Ling of Wei, saying, "Your Majesty, that's wonderful! I thought Wei had only one virtuous man, Qu Boyu, but now there are at least two. Congratulations on gaining another worthy minister."
Duke Ling of Wei, left with no other choice, reluctantly revealed the truth to Nanzi.
Later, the idiom "not deceiving in a dark room" came to describe someone who refrains from doing wrong even when no one is watching or knows.
Source: *Biographies of Exemplary Women*
Meaning of the Idiom: Later, the Chinese idiom "不欺暗室" came to describe how someone refrains from doing wrong even when no one is watching or knows.