春秋時，虞、虢兩國緊鄰著晉國，晉國一直想併吞他們。晉獻公就利用名馬和寶玉來收買虞公，讓他答應借路，方便晉國攻打虢國，甚至虞公還派兵幫晉軍帶路，晉國因此順利攻下虢國的下陽。三年後，晉國又再度向虞國借路去攻打虢國，這時虢國大夫宮之奇便勸諫虞公說：「輔車相依，唇亡齒寒」，並說明虞和虢兩國之間的利害關係，希望虞公不要再借路，而應該兩國聯合起來對抗晉國。虞公不聽，還是借路給晉國，這時，宮之奇便預言：「虞和虢會同歸於盡，等不到過年就會滅亡。」說完便帶著家人逃到別國。果然，過年前一個月，晉國滅了虢國，虢公逃到洛陽。晉軍回程時，趁虞國沒有防備心，發動突襲，輕易地把虞國也消滅了。
三十六計之第二十四計：假途伐虢
指用對方給自己的方便，來掩飾自己的企圖，趁機再擴大自己的勢力範圍，達到真正想要的目的。
In the Spring and Autumn Period, the small states of Yu and Guo were bordering the larger state of Jin. Jin always wanted to conquer these two neighboring states.
To this end, Jin Sian Gong used fine horses and jewelry to bribe the duke of Yu in exchange for safe passage for his army to pass through his country to attack Guo. The duke of Yu accepted his offer and even sent troops to lead the way. The Jin army was able to conquered the city of Sia Yang smoothly.
Three years later, Jin made the same request to the duke of Yu again. One of the senior officials of Guo, Gong Jhih Ji, cautioned the duke of Yu against accepting Jin's request by saying, "Yu is to Guo, as lips are to teeth. If the lips are gone, the teeth will be exposed to the cold." He explained the mutually dependent relationship between Yu and Guo, hoping that the duke of Yu would refuse Jin's request for safe passage. Instead, both Yu and Guo should unit together to fight Jin. Despite Gong Jhih Ji's warning and advice, the duke of Yu chose to ignored him and agreed to Jin's request for safe passage. Gong Jhih Ji thus predicted that both Yu and Guo will would be destroyed together before the end of the year.'' That said, he took his family and fled to another country.
Indeed. a month before the end of the year, Guo was conquered by Jin. And on their way back through Yu, the Jin army launched a surprise attack on the unsuspecting Yu. As a result, Yu, too, was easily conquered by Jin.
Strategy 24: Obtain Safe Passage to Conquer Guo
Using the convenience given by your enemy to cover up your real intentions and to increase your power in order to achieve your ultimate goal.
