[Source] Sima Guang's "Zizhi Tongjian" (Comprehensive Mirror to Aid in Government) from the Song Dynasty.
[Meaning] "Jar" refers to a large earthenware pot with a narrow mouth and wide belly. The phrase literally means "inviting you into the jar," using your own method to punish yourself. It is a metaphor for using someone's own tactics against them to deal with them.
[Historical Anecdote]
During Empress Wu Zetian's reign, she implemented a policy of terror and high pressure, rewarding informers, through which many people gained promotions and higher ranks. At that time, numerous cruel officials emerged, inventing all kinds of brutal torture devices to force suspects to confess—truly employing every possible extreme method. Among them, Zhou Xing and Lai Junchen were the most notorious.
Zhou Xing, who took pleasure in torturing others day after day, never imagined that one day he himself would become the target of denunciation. After receiving an anonymous letter accusing Zhou Xing of conspiring rebellion with others, Empress Wu flew into a rage and immediately issued a secret edict to Lai Junchen, ordering him to handle the case.
When the eunuch delivered the secret decree, Zhou Xing was drinking with Lai Junchen! The two were chatting over drinks about methods to extract confessions. After reading the decree brought by the eunuch, Lai casually tossed it onto the table and continued discussing the previous topic with Zhou. Lai mentioned that he had written a book titled "The Manual of Fabricating Charges." Zhou laughed and said the punishments described in it were nothing special; recently, he had thought up a new, excellent method to force suspects to confess. Lai asked, "What method?"
Zhou proudly replied, "This new method involves taking a large jar, placing it over a fire to heat it up. Anyone who refuses to confess will be put inside the hot jar—how could they not confess?" Lai Junchen exclaimed approval repeatedly. As he spoke, he ordered attendants to bring a large jar and a brazier full of burning charcoal into the hall, placing the jar on top of the brazier, where the charcoal blazed fiercely.
Lai Junchen felt the moment had come. He suddenly changed his expression, sternly read out Empress Wu’s secret decree to Zhou Xing: "Zhou Xing, listen well! If you don't honestly confess, then we'll just have to invite you into this jar!"
Zhou Xing instantly turned pale with fright, utterly terrified, dropping his wine cup to the floor. He quickly knelt down and declared his willingness to confess. Lai Junchen sentenced him to death and reported the verdict to Empress Wu. Considering that Zhou Xing had done much for her, Wu spared his life, instead sentencing him to penal servitude. However, Zhou had made too many enemies; on his way to exile, he was murdered by his foes.