出自《战国策·赵策一》，记住以前的经验教训，将它作为今后做事的借鉴。师：师表、榜样，引申为鉴戒。
From the Strategies of the Warring States – Strategies of Zhao. Remembering the experiences and lessons of the past, and using them to provide guidance for future endeavors.
春秋战国时期，晋国的大权被智、赵、魏、韩四卿瓜分。后来，智卿智伯独揽了朝政大权，成为晋国最大的卿。其他三卿赵襄子、魏桓子和韩康子因为实力不济，都不敢和他抗衡。
During the Spring and Autumn and Warring States periods, the power of the State of Jin was divided among the four noble families of Zhi, Zhao, Wei and Han. Later, the Zhi nobleman Zhi Bo monopolized state power and became Jin’s foremost minister. The other three ministers – Zhao Xiangzi of Zhao, Wei Huanzi of Wei and Han Kangzi of Han – did not dare defy him due to their weaker positions.
智伯为扩大地盘，分别向三卿讨要土地。魏桓子和韩康子都不敢违抗智伯的命令，乖乖地献上了土地。赵襄子却坚决不肯献出土地。智伯非常生气，就打算联合魏桓子和韩康子一起攻打赵襄子。
To expand his territory, Zhi Bo demanded land from the three other nobles. Wei Huanzi and Han Kangzi dared not disobey and offered up land. But Zhao Xiangzi of Zhao resolutely refused to cede land. Furious, Zhi Bo planned to ally with Wei and Han to attack Zhao Xiangzi.
赵襄子知道智伯不会轻易放过他，就找来谋臣张孟谈商讨对策。张孟谈指出，魏桓子和韩康子虽然表面顺从智伯，但其实心里对智伯十分憎恨，如果联合他们一起对付智伯，那么就一定可以打败智伯，守住赵国的领土。
Realizing Zhi Bo would not easily let him off, Zhao Xiangzi consulted the strategist Zhang Mengtan for advice. Zhang pointed out that although Wei and Han outwardly obeyed Zhi Bo, they deeply resented him. If allied against Zhi Bo, they could certainly defeat him and preserve Zhao’s lands.
赵襄子按照张孟谈的方法去做，结果活捉了智伯。从此，晋国成了赵、魏、韩三家鼎立的局面。
Following Zhang’s plan, Zhao Xiangzi ended up capturing Zhi Bo alive. From then on, the three households of Zhao, Wei and Han held equal power in Jin.
张孟谈为赵国立了大功，他不但没有接受赏赐，反而提出离开的请求。赵襄子急忙挽留。张孟谈说：“我知道大王打算报答我，但我这次立了大功，我的名声可能会超过你。我从治国角度考虑，才提出离开的。在历史上从来没有君臣权势相同而永远和好相处的。我们这些后人不能忘记以前的教训啊！”
Though Zhang had made an great contribution to Zhao, instead of accepting rewards, he requested to leave. Zhao Xiangzi urgently tried to keep him. Zhang said, “I know the lord intends to reward me, but my great achievement may make my reputation outshine yours. From the perspective of governing, I make this request to leave. In history, there are no examples of a lord and minister with equal power living in harmony forever. We descendants cannot forget these past lessons!”
赵襄子觉得张孟谈的话很有道理，只得答应了他的请求。
Seeing the wisdom in Zhang’s words, Zhao Xiangzi had to agree to his request.