To Repair The Fence After Losing The Sheep

King Shiang, ruler of the Kingdom of Ch'u during the Warring States Period, was concerned only with enjoying himself, and paid no attention to the affairs of the state. His minister, Juang Shin, was very worried, and said to him, "His Majesty has four officials who are constantly at his side, keeping him comfortable and amused. If things continue in this way, I fear for Ch'u's future." King Shiang grew very angry and rebuked Juang Shin. And the minister, seeing he could not get through to the king, requested permission to go to the kingdom of Chao.

Less than six months later, the kingdom of Ch'in captured several Ch'u cities, and King Shiang fled to Chengyang. When he thought of Juang Shin, he was overcome with regret, and immediately sent someone to go find him. Juang Shin urged the king not to worry, saying "Even after you've lost the sheep, it's still not too late to repair the fence!" So the king put all of his effort into helping his state, and with Juang Shin's guidance, Ch'u survived.

Thus, "To Repair the Fence After Losing the Sheep" is to repair a flaw or correct a shortcoming, so that one will not make the same mistake twice.

亡羊補牢

山腳下住著幾戶人家，養著鷄、羊，種些蔬、果。

有一天，李家的阿齊突然驚慌的到處報告鄰居說：「唉呀！我走失了一頭羊，
拜託幫我找找！」

大夥兒聽說阿齊走我了一頭羊，都擱下自己的工作去找羊，一直到太陽下山
看不見路，仍然沒有找著。大夥兒圍著阿齊問：「羊怎麼會走丟的？」
阿齊指著羊欄的一個破口說：「欄柵斷，我忘了補。」
年紀最長的方老爺子對阿齊說：「亡羊補牢，猶未晚矣。」
意思就是說，羊雖走丟了，如果趕緊補好羊欄，還不太晚。比喻錯誤發生了，如果及時挽救，仍有成功的可能。「亡」是走失的意思，「牢」指養牲的欄。

此句成語原來起源戰國時代的一個故事，記載在「戰國策」，這本書專門寫一些辯士向君主貢獻的策略。