In 626 AD, after Emperor Taizong of Tang, Li Shimin, ascended the throne, he implemented a series of measures to revitalize governance and strengthen the state, with one crucial policy being to open wide the channels for advice and humbly listen to his ministers' opinions.
During the Tang Dynasty, the imperial advisor Wei Zheng was the most outspoken minister in the court. Whenever he spotted Emperor Taizong making a mistake, he would point it out without mercy, and even when the emperor grew angry, Wei Zheng would remain calm and finish his critique.
One day, Emperor Taizong of Tang was playing with a hunting falcon when his stern advisor Wei Zheng arrived to report on state affairs. Fearing Wei Zheng would lecture him about his pastime, Taizong quickly stuffed the falcon into his robe. Wei Zheng, noticing the emperor's awkwardness, deliberately prolonged his report with lengthy details. By the time he finished, Taizong pulled out the falcon—only to find it had suffocated to death.
Soon after, Taizong faced another blunt criticism from Wei Zheng in court and was furious. Returning to the palace, he fumed, "One day, I will kill this country bumpkin!"
Empress Zhangsun heard this and asked who he wanted to kill. Taizong replied, "Wei Zheng always embarrasses me at court..."
Upon hearing this, Empress Zhangsun immediately changed out of her casual clothes, donned her full ceremonial regalia, and bowed to Emperor Taizong in congratulations.
Emperor Taizong asked in surprise, "What are you doing?" Empress Zhangsun replied, "As the saying goes, 'When the ruler is wise, his ministers are upright.' The reason Wei Zheng is so outspoken is precisely because Your Majesty is wise. How could I not offer my congratulations?"
Emperor Taizong's anger then turned to joy, and he no longer resented Wei Zheng. He often summoned Wei Zheng to his chambers to discuss state affairs. Once, Taizong asked Wei Zheng, "What makes a wise ruler, and what makes a foolish one?"
Wei Zheng replied, "Listen to both sides and you will be enlightened; heed only one side and you will be benighted. The ancient sage-kings Yao and Shun listened to the views of the common people, so they knew where villains were causing harm and were hailed as sages by later generations. The Second Emperor of Qin heeded only the eunuch Zhao Gao, which led to the fall of the Qin dynasty. Such examples are many. Therefore, an emperor must gather opinions from all sides, not trust only one person, to ensure long-term peace and stability."
Emperor Taizong nodded repeatedly, saying, "You are absolutely right." From that day on, his trust in Wei Zheng only deepened.
Later, the idiom "Listen to both sides and you will be enlightened; heed only one side and you will be benighted" came to describe how considering multiple opinions clarifies truth, while relying on a single view obscures it.
Source: *Zizhi Tongjian*, Chapter "The Second Year of Emperor Taizong of Tang's Zhenguan Reign"
Meaning of the Idiom: Later, the Chinese idiom "兼听则明，偏信则暗" came to describe how considering multiple opinions clarifies truth, while relying on a single view obscures it.