During the early Spring and Autumn period, the Zhou dynasty's power had already severely declined, and King Ping of Zhou, the Son of Heaven, was utterly incompetent, with the reins of government firmly in the hands of the chief minister, Duke Zhuang of Zheng.
King Ping of Zhou, deeply frustrated by the erosion of his royal authority, sought to curb Duke Zhuang of Zheng's power by inviting the Duke of Guo to serve as his chief advisor.
When Duke Zhuang of Zheng learned of this, he flew into a rage. King Ping of Zhou, terrified, explained to Duke Zhuang that he had no intention of letting the Duke of Guo replace him as chief minister. To win Duke Zhuang's trust, the king proposed exchanging hostages: his own crown prince, Hu, would go to Zheng as a hostage, while Zheng's prince, Hu, would come to the Zhou court as a hostage.
In 720 BCE, King Ping of Zhou died, and his grandson Ji Lin ascended the throne as King Huan of Zhou. Distrustful of Duke Zhuang of Zheng, King Huan planned to appoint Duke Guo as chief minister to take over state affairs. Enraged, Duke Zhuang twice sent generals to raid Zhou territory and seize their wheat harvest. From then on, relations between Zhou and Zheng soured further, and the Eastern Zhou Dynasty existed in name only.
Later, the author of *Zuo Zhuan* commented on this event: Insincere words and lack of genuine trust make even the exchange of hostages useless!
Later, the idiom "yan bu you zhong" came to describe words that do not come from the heart, meaning one's speech is insincere.
Source: *Zuo Zhuan*, "Duke Yin, Year Three"
Meaning of the Idiom: Later, the Chinese idiom "言不由衷" came to describe words that do not come from the heart, meaning one's speech is insincere.