戰國時期，楚襄王統治楚國時，國勢不振。楚王和重要的大臣都荒淫無能。他們一直沉溺于奢侈享樂之中。大臣莊辛預見到楚國會發生危險。一天他勸諫楚王說：" 陛下，無論你走到哪兒，身旁總是那些奉承你的人，他們想盡辦法讓您高興，您就忘了處理國事。長此以往，國家遲早會滅亡的。"

　　楚王大怒："大膽！你居然用這樣惡毒的話來詛咒我的國家，蓄意挑起人民的不滿！" 莊辛解釋說："我不敢詛咒楚國，但我可以預言楚國正面臨著巨大的危險。" 莊辛見楚王如此寵信那些腐敗的大臣，相信楚國必定要亡國。于是他向楚王請求離開楚國，到趙國居住一段時候。

　　楚王同意了，他便到趙國去了。五個月之后，秦君果然派軍入侵楚國，占領了大片土地。楚王被迫流亡。這時，他想起了莊辛的勸諫，于是派人接莊辛回來。楚王見了莊辛，便問："現在我該怎么辦呢？"

　　莊辛回答說："丟了羊，就把羊圈修好，不算遲。" 然后他提出許多如何重振國家，收復失地的好謀略。楚王非常高興。

　　成語"亡羊補牢"就是由莊辛對楚王的回答而來的。比喻事情出了差錯，有了損失，如果及時補救，還能夠彌補，吸取教訓。

　　Mend the fold after a sheep is lost

　　During the Warring States Period (475-221 BC)， the State of Chu not very powerful. The king and the important court officials were dissolute and incompetent. They indulged in luxury and excessive pleasure all the time. Zhuang Xin, one of the ministers foresaw that the country was in danger. One day he remonstrated with the king: "Your Majesty, wherever you go, you’re always surrounded by people who flatter you with what you like. They try everything to make you happy so that you forgot to tend to state affairs. If you go on like this, no doubt, the country will perish sooner or later."

　　The King of Chu flew into a rage. "How dare you! You even use such vicious words to curse my country and mean to arouse resentment among the people!" Zhuang Xin explained, "I dare not curse the State of Chu. But I really have a premonition that Chu is facing great danger." Seeing that the king is especially fond of those corrupt officials and trust them in everything, the minister thought Chu is bound to extinct. So he asked the king to let him leave Chu. He wanted to go to the State of Zhao and stay there for a while.

　　The king gave him the leave.

　　Five months later, the King of Qin sent his troops to invade Chu and occupied a large tract of its territory. The King of Chu himself went into exile. Now, the king remembered Zhuang Xin’s words. He sent his men to fetch him. When the king saw Zhuang Xin again, he asked him, "What can I do now?"

　　Zhuang Xin replied, "It’s not too late if you mend the sheepfold when you find a sheep is missing." He then made some good suggestions to rehabilitate the state and recover the lost land. The king was very much pleased.

　　The idiom "Mend the fold after a sheep is lost" has developed from Zhuang Xin’s answer to the king.

　　We still use this metaphor to advise someone that even when he has made a mistake and suffered losses, he can still remedy it by drawing lessons from the mistake.