During the Spring and Autumn period, the great states were locked in brutal wars for supremacy.
In 562 BCE, Duke Dao of Jin launched an attack on the state of Zheng. Duke Jing of Qin, responding to Zheng's plea for help, sent his army to rescue them and crushed the Jin forces at Li. This battle turned the long-allied states of Qin and Jin—bound by generations of marriage—into bitter enemies.
Three years later, Duke Dao of Jin, seeking to avenge past humiliation, united twelve states including Qi, Lu, Song, Wei, and Zheng to launch a campaign against Qin. The Jin army's Grand General Xun Yan took command, leading the entire force.
Although the allied forces were numerous, being a patchwork from over a dozen states, their unity was inevitably lacking. When the troops reached the banks of the Jing River, each state's army hesitated, unwilling to cross first. Xun Yan grew deeply anxious.
Later, the armies of Ju and Lu crossed the river first, and seeing someone take the lead, the other states followed suit one after another.
When Duke Jing of Qin saw the allied armies camped near the Jing River, he ordered his men to poison the river upstream. Many soldiers from the allied forces drank the water and died from the poison. Panic spread through the camps, and the allies dared not make any move.
The prince of Zheng refused to linger, ordering his troops to march, and only then did the allied armies follow, setting up camp at Yulin in Qin territory.
Xun Yan had assumed that the imposing coalition of twelve states would surely force Qin to sue for peace. To his surprise, Qin had already discovered that the allied forces were divided in spirit, so they showed no fear, let alone any intention of negotiating.
Xun Yan, furious, immediately issued a military order: "Harness the chariots at cockcrow, fill the wells and level the stoves, and look only to my horse's head for direction."
This means: When the rooster crows, we move—fill in wells, level stoves, and the whole army follows my horse's head wherever I lead.
Unexpectedly, Luan Yan, the commander of Jin's lower army, was deeply dissatisfied with Xun Yan's monopoly on power and fumed, "Why should we listen to him? No way! If he heads west, I'll go east!"
With that, he led his troops back to the state of Jin.
Xun Yan, caught between laughter and tears, sighed to the heavens, "My order was too harsh—that was my fault. But military commands are as unshakable as mountains; once issued, they cannot be withdrawn. Since the order cannot be carried out, our army is doomed to defeat in battle!"
Xun Yan then announced loudly, "The entire army retreats!" His miscalculation of internal conflicts within the ranks and his unrealistic demand that his subordinates "look only to the horse's head for direction" resulted in a "defeat without battle," which later became a laughingstock. Over time, the idiom "look only to the horse's head" came to mean following orders or willingly following someone's lead.
Source: *Zuo Zhuan*, Chapter "Duke Xiang's Fourteenth Year"
Meaning of the Idiom: Later, the Chinese idiom "马首是瞻" came to describe following orders or willingly following someone's lead.