In 594 BCE, King Zhuang of Chu sent his envoy Shen Zhou (also known as Shen Wuwei) through the state of Song on a mission to Qi. According to the customs of the time, passing through another state required its permission, but Chu, confident in its strength, did not openly seek Song's consent. The state of Song saw this as a deliberate insult, sparking deep resentment. In response, Song detained Shen Zhou and executed him.
When King Zhuang of Chu heard that Shen Zhou had been killed, he leaped to his feet in fury, dashing into the courtyard before his attendants could even slip on his shoes, racing out the palace gate before his sword was buckled, and reaching the street before his chariot was ready. As Shen Zhou had arranged before his mission, the king personally led the army to attack Song, swiftly surrounding the state entirely.
At this critical moment, the State of Song dispatched Minister Yue Yingqi to the State of Jin to urgently request reinforcements. Duke Jing of Jin, confident in his kingdom's formidable strength, feared that refusing to send troops would invite ridicule, so he prepared to march to Song's rescue.
But Bo Zong, a high-ranking official of the State of Jin, opposed sending troops and advised against it, saying, "As the ancients said, 'Though the whip is long, it cannot reach the horse's belly.'" He explained that the horse's belly is not where a whip should strike, meaning that the State of Chu was not a proper target for Jin's attack. "Chu is at the height of its power," Bo Zong continued, "and contending with them would only bring harm, not benefit. We must carefully weigh the pros and cons, understand the need for flexibility, and keep a clear assessment of the situation."
Bo Zong continued, "There is a folk saying: 'One must weigh circumstances in the heart; rivers and marshes accept filth, thickets and wetlands harbor venom, fine jade conceals flaws, and a ruler must endure disgrace—this is the way of heaven.'" He explained, "This means we must assess situations and keep our judgment clear. Rivers and lakes can hold impurities, forests and grasslands hide snakes and beasts, and even precious jade may have blemishes. A ruler must tolerate insults and humiliation—it is a natural principle. So there is no need to fret over being mocked for not sending troops to rescue the Song state."
After hearing Bo Zong's persuasive reasoning, Duke Jing of Jin found it quite sensible and abandoned his plan to send troops to rescue the Song state.
"The idiom 'Gao Xia Zai Xin' (literally 'high and low in the heart') is a metaphor for knowing one's limits and being able to bend or stretch as needed; later, it also came to mean having the initiative and acting with ease."
Source: *Zuo Zhuan*, "Duke Xuan's Fourteenth Year"
Meaning of the Idiom: Later, the Chinese idiom "高下在心" came to describe knowing one's limits and being able to bend or stretch as needed; later, it also came to mean having the initiative and acting with ease.