During the final years of the Tang Dynasty, Emperor Xizong could no longer control the realm as regional military governors, known as jiedushi, carved out their own independent territories. These warlords schemed against one another, each vying to seize cities and lands, locked in a relentless struggle where every faction sought to devour its rivals.
During the Tang Dynasty, the military governor Luo Shaowei controlled six prefectures including Weizhou, commanding considerable power, yet he lived in constant fear because his personal guard—a fierce and arrogant force—refused to follow orders, and he dreaded that one day they might rebel, kill him, and install a new commander.
Determined to eliminate this threat, he sent his trusted aide Zang Tingfan to meet with his in-law, Liang King Zhu Quanzhong, requesting Zhu Quanzhong's assistance in wiping out his own personal guard.
Zhu Quanzhong, originally named Zhu Wen, began as a general in the Huang Chao rebellion. He later betrayed the rebels, surrendered to the Tang court, and crushed the uprising he once fought for. Emperor Xizong rewarded him by appointing him military governor of Xuanwu, bestowing the name "Quanzhong" (meaning "Loyal to All"), and soon after granting him the title Prince of Liang.
When Zhu Quanzhong met Zang Tingfan, he agreed to send troops to help Luo Shaowei eliminate his rivals. Coincidentally, Zhu Quanzhong's daughter had just died, so he used her funeral as a pretext, ordering soldiers to hide weapons in luggage chests and march into Weizhou. Meanwhile, Luo Shaowei secretly sabotaged the weapons and armor stored in the armory, then caught the guards off guard with a pincer attack from inside and out, annihilating the entire guard force.
After Zhu Quanzhong helped Luo Shaowei eliminate his personal guard, he stationed his troops in Weizhou, acting as if he were the master of the region. Parading as the supreme commander, he inspected everywhere and roamed about under the pretext of suppressing rebellions and restoring order. Yet his army's provisions were entirely Luo Shaowei's responsibility. Within just half a year, Luo slaughtered 700,000 cattle and sheep and supplied over a million taels of silver for military pay, draining all of Weizhou's reserves.
Luo Shaowei, though he used Zhu Quanzhong to eliminate threats around him, had invited a wolf into his home, effectively handing Weizhou over to Zhu Quanzhong. He deeply regretted this and sighed, saying:
"Even if you gathered all the iron from the six prefectures and forty-three counties of Weibo, you couldn't cast a mistake this big!" Here, "mistake" is a pun, borrowing the word for "engraving error" to mean a great blunder.
Later, the idiom "to cast a great mistake" came to be used to refer to making a major error.
Source: *Zizhi Tongjian*, "Tang Records"
Meaning of the Idiom: Later, the Chinese idiom "铸成大错" came to describe how to refer to making a major error.