赵国的平原君，他培养了许多有本领的人，这些人随时准备为他做事。
当时称这些人为食客。
有一次，秦国攻打赵国，情况危急。
平原君打算向楚国求救。
他要从众多食客中选出二十个能文善武的人，跟着他一起去楚国，说服楚王采用合纵策略，合力抗秦。
但是他挑选到最后，只能选出十九人。
正在烦恼的时候，一个名叫毛遂的食客自己站出来说：“让我跟随您去楚国吧！”
平原君虽然对毛遂没有信心，还是答应了他的请求！
到了楚国，任凭平原君怎么努力地游说楚王，甚至从日出谈到中午，还是没有得到满意的结果。
最后，身上佩着剑的毛遂突然登上台阶，来到楚王和平原君的面前。
楚王大声喝道：“你如此斗胆，还不退下！你在干什么？”
毛遂按剑上前，对楚王说：“贵国虽然人多，但现在的情形是这样的，十步之内，没有人能保护你，而你的性命就在我的手上。”
接着他针对联合抗秦的好处，一一说明。
楚王连声说：“对！对！”
并且马上在殿上和赵国定下了合作抗秦的决议。
平原君回到赵国后，赞赏毛遂，说：“先生对楚王的一番说话，就像九鼎和大吕钟一样，份量十足，使我们的国家大受重视。”
后人就以“一言九鼎”这句成语来形容很有份量的一句话，就像九鼎那么重。
Zhao Guo's Pingyuanjun, he cultivated many capable people, who were always ready to do things for him.
At that time, these people were called guests of food.
Once, Qin State attacked Zhao State, and the situation was critical.
Pingyuanjun planned to seek help from Chu State.
He wanted to select twenty men who could write and fight from among the many food guests, and follow him to Chu State to persuade King Chu to adopt the strategy of coalition and work together to resist Qin.
But when he picked until the end, he could only choose nineteen people.
When he was worried, a food guest named Mao Sui came forward and said, "Let me go with you to Chu State!"
Although Pingyuanjun had no confidence in Mao Sui, he still agreed to his request!
Arriving in Chu State, despite Pingyuanjun's efforts to persuade King Chu, even talking from sunrise to noon, there was still no satisfactory result.
Finally, Mao Sui, who was wearing a sword, suddenly stepped onto the steps and came to the front of King Chu and Pingyuanjun.
King Chu shouted loudly, "How dare you be so bold, don't retreat yet! What are you doing?"
Mao Sui approached with his sword and said to King Chu, "Although your country has many people, the situation is such that within ten steps, no one can protect you, and your life is in my hands."
Then he explained the benefits of joint resistance to Qin one by one.
King Chu repeatedly said, "Yes! Yes!"
And immediately made a resolution of cooperation with Zhao State on the spot.
After returning to Zhao State, Pingyuanjun praised Mao Sui, saying, "The words you said to King Chu were as heavy as nine tripods and the Da Lu bell, giving our country great importance."
Later generations used the idiom 'one word is as heavy as nine tripods' to describe a very weighty sentence, like nine tripods.
