According to Records of the Historian Volume 76 Biography of Yuqing in Ping Yuanjun, Ping Yuanjun, during the Warring States Period, the State of Qin sent troops to attack Zhao and surrounded Handan, the capital of Zhao. The situation was very critical, so the prince of Zhao sent Ping Yuanjun to Chu for help. Ping Yuanjun planned to select 20 talents with both civil and military skills to go with his diners, but only 19 were selected, and the rest were unqualified. At this time, a man named Mao Sui volunteered to recommend himself to Ping Yuanjun and asked to join the ranks of Chu. Ping Yuanjun asked, "How long have you been under my door?" Mao Sui replied, "Three years." Ping Yuanjun said: "A truly talented person, like an awl in a bag, will immediately show its sharp point. And you have been under my door for three years, but I have never heard your performance. You'd better stay! " Mao Sui said: "I am recommending myself now, that is, please put me in the bag. If I had such an opportunity earlier, I could not only show my talent, but also show my edge! " Ping Yuanjun thought Mao Sui had a point, so he promised to let him go with him. In the State of Chu, Ping Yuanjun held talks with the King of Chu, but there was no result from morning till noon. So Mao Sui took a sword to see the king of Chu, trying to explain the interests of Zhao and Chu in the joint resistance to Qin. The king of Chu was finally persuaded and promised to send troops to Zhao for rescue. So the two countries forged a blood alliance on the spot and vowed to keep the Covenant of common resistance to Qin. Mao Sui not only helped Ping Yuanjun finish the task this time, but also made contributions to the country, making everyone sit up and take notice of him, so Ping Yuanjun treated him as a distinguished guest. Later, this story was condensed into the idiom "recommend yourself", which means to be a volunteer and recommend yourself.