During the early Warring States period, the seven kingdoms fought for supremacy, with the western state of Qin being the most powerful, casting a covetous eye on the six eastern states. A man named Su Qin decided to lobby the six states with his strategy of "vertical alliance" to resist Qin.
That day, he arrived in the state of Han, where King Han was discussing a major matter with his ministers. It turned out that a few days earlier, Zhang Yi of Wei had urged the king to adopt the "horizontal alliance" strategy and join forces with Qin. King Han, seeing Qin as a predatory state with vast ambitions, dared neither to offend it nor to ally with it, and was still wavering in indecision.
After Su Qin explained his purpose to the King of Han, the king said with a troubled expression, "To be honest with you, Zhang Yi also came, asking me to ally with Qin." Su Qin asked anxiously, "Did Your Majesty agree?" "Alas!" The King of Han sighed noncommittally.
"Great King," Su Qin stepped forward and said, "The world knows the King of Qin harbors imperial ambitions. Qin's feathers are not yet full-grown, so it uses sweet words to win over the six states. When the time is ripe, it will swallow you one by one. Do not fall for its tricks!"
King Han nodded, "I understand what you say, sir, but I fear offending Qin, for our state of Han borders it, and it would be easy for them to attack us."
Su Qin countered, 'What's there to fear? Even the strongest fists can't beat four hands—if the six states unite, Qin won't dare act rashly. Besides, Han has fortified castles, strategic terrain, elite weapons, and brave troops, along with a wise and virtuous ruler like you. Why should you bow to Qin? If Your Majesty heeds Zhang Yi's advice and allies with Qin, you'll be admitting defeat. Then Qin will mold Han like dough, demanding Yiyang and Chenggao one moment, other lands the next. Han's territory is finite, but Qin's greed knows no bounds—it can destroy Han without lifting a sword. As the saying goes, "Better to be a chicken's beak than a cow's rear." If you join Qin, you'll cease to be a sovereign and become that "cow's rear"!'
After hearing Su Qin's words, the King of Han angrily rolled up his sleeves, reached for the sword at his waist, and said, "I would rather die than ally with Qin. I am willing to join the other five states in a vertical alliance against Qin!"
Later, the idiom "Better to be a chicken's beak than a cow's rear" (preferring the small but clean beak over the large but foul anus) came to mean preferring autonomy in a small scope over being dominated in a larger one.
Source: *Strategies of the Warring States*, Chapter "Strategy for Han I"
Meaning of the Idiom: Later, the Chinese idiom "宁为鸡口，无为牛后" came to describe preferring autonomy in a small scope over being dominated in a larger one.