During the Spring and Autumn period, a Qin official named Qizi, stationed in Zheng, secretly sent word to Duke Mu of Qin: "I now control the defense of Zheng's Beixia Gate. If you launch a surprise attack, Zheng will be yours." Duke Mu sought advice from his veteran minister, Jian Shu, who warned, "Marching an army over such a distance to strike a far-off state violates military doctrine—it will surely fail." Ignoring this, the Duke ordered generals Meng Mingshi, Xiqishu, and Bai Yibing to lead the troops. Jian Shu stopped them on the road, weeping, and told the generals, "You will never return!" Enraged, Duke Mu sent a messenger to scold Jian Shu: "Old fool, what do you know? If you had died at sixty or seventy, the trees on your grave would already be as thick as a bowl!"
Jian Shu ignored the man and said to his son who was accompanying the army on the expedition, "The Qin army's surprise attack on Zheng will pass through the Xiao Mountains on the border of Jin, where the terrain is extremely treacherous. If your surprise attack on Zheng fails, you will surely be ambushed by the Jin army there on your return. I will have to go there to collect your corpse."
As Uncle Jian had predicted, the Qin army's surprise attack failed. On their retreat, they were ambushed by the Jin forces at Mount Xiao, suffering a crushing defeat. The three generals, including Meng Mingshi, were captured alive.
Later, the idiom "Laoshi Xiyuan" came to refer to risky military operations.
Source: *Zuo Zhuan*, Chapter "Duke Xi's Thirty-Second Year"
Meaning of the Idiom: Later, the Chinese idiom "劳师袭远" came to describe risky military operations.