Posted 2017/6/14
Before the First Emperor of Qin unified China, Li Si, a native of the State of Chu, went to the State of Qin, where he was employed as a court official. Later, the State of Han sent a man named Zheng Guo to Qin to persuade its ruler to build an irrigation canal. Han's real aim was to make Qin consume much manpower and resources in the project and render it incapable of invading Han. The ruler of Qin fell for this ruse, and built a canal called Zhengguo Canal. Later, Han's real intention was discovered and the advisers of the ruler urged him to expel all the foreign officials. Li Si was among those who were to be expelled. He sent a petition to the King, explaining that expelling all foreign officials would be disadvantageous to Qin. As a result, the ruler of Qin canceled the command. Li Si stayed in Qin, became the premier and subsequently helped it to conquer the whole country.
Later, the request for guests to leave came to be called "order for guest to leave".
