During the Warring States period, Su Qin initially advocated for "horizontal alliances" and went to the state of Qin to persuade King Hui of Qin. He exhausted his efforts in Qin, submitting ten memorials, but failed to sway the king, and his proposal was not adopted.
His black mink robe was worn threadbare, his hundred catties of gold were spent, and all his provisions were gone—Su Qin had no choice but to leave the state of Qin and return to his hometown of Luoyang.
At that time, Su Qin wore straw sandals, carried a book chest, his face haggard, body gaunt, eyes sunken and dark, with a look of shame upon his countenance.
After his humiliating defeat in Qin, Su Qin was deeply shaken, convinced that the King of Qin had caused his misfortune. That very night, he scoured every book in his home until he found a military treatise. He buried himself in study, practicing its strategies relentlessly. When drowsiness overtook him late at night, he would grab an awl and stab himself in the thigh, drawing blood that often trickled down to his feet, just to stay awake. After a full year, he had memorized the entire text and could apply its lessons with ease.
So Su Qin modeled his strategy on the chapter "Swallows Gathering at the Watchtower" and went to the State of Zhao, where he met with the King of Zhao in his summer palace. He passionately presented his "Vertical Alliance" plan, hoping to unite the six states east of Mount Yao against Qin. The two talked with great rapport, and in their excitement, they clapped their hands loudly at each other.
The King of Zhao was thrilled, appointing Su Qin as Lord Wu'an, granting him the prime minister's seal, and bestowing a hundred chariots, a thousand bolts of embroidered silk, a hundred pairs of white jade discs, and ten thousand yi of gold. He kept Su Qin by his side to strategize the alliance of the six states against Qin's divide-and-conquer tactics.
Su Qin's "Vertical Alliance" strategy was unanimously supported by six states, and he wore the seals of all six. Later, the idiom "talking palm to palm" came to describe unrestrained, cheerful conversation.
Source: *Strategies of the Warring States*, Chapter "Strategy for Qin I"
Meaning of the Idiom: Later, the Chinese idiom "抵掌而谈" came to describe unrestrained, cheerful conversation.