The idiom "Bu De Yao Ling" literally means "cannot grasp the waist and collar." "Yao" (要) means waist, referring to the waistband of clothing; "Ling" (领) means collar. In ancient times, people wore separate upper and lower garments. When lifting the upper garment, one would hold the collar; when lifting the lower garment, one would hold the part near the waist. "Yao ling" (waist and collar) metaphorically refers to the essence or main point, here extended to mean attitude or intention. Today, this idiom generally describes speech or writing that fails to grasp the essential points or key issues.
This idiom originates from the "Records of the Grand Historian: The Account of Dayuan": "Qian went from Yuezhi to Daxia, but ultimately could not obtain the essential stance of Yuezhi."
When Emperor Wu of Han first ascended the throne, defectors from the northern Xiongnu tribes all said that the Xiongnu had defeated the Yuezhi (yuezhi), used the skull of the Yuezhi king as a large wine cup, driven the Yuezhi people away, and that the Yuezhi harbored intense hatred towards the Xiongnu. They wanted to attack the Xiongnu but could not get assistance from other nations.
At the time, Emperor Wu was eager to eliminate the Xiongnu. Hearing this, he wished to establish friendly relations with the Yuezhi. However, to reach the Yuezhi, one had to pass through Xiongnu territory, so he recruited envoys willing to journey to Yuezhi. Zhang Qian, who had only recently become a court official, volunteered for the mission and was approved by the emperor.
Unfortunately, when Zhang Qian passed through Xiongnu territory, he was captured and taken to the Chanyu (Xiongnu leader). The Chanyu detained Zhang Qian and said to him: "Yuezhi is to our northwest. How can you Han people send an envoy there? If we wanted to send an envoy to Yue, would you let us pass?"
Thus, Zhang Qian was held captive by the Xiongnu for over ten years. The Xiongnu gave him a wife and he had a son, but Zhang Qian always kept the imperial staff of office given to him by the Han court.
Later, the Xiongnu relaxed their surveillance over Zhang Qian. He then escaped with his attendants, heading in the direction of Yuezhi. After traveling for dozens of days, they arrived in the kingdom of Dayuan. The king of Dayuan had heard that the Han dynasty was extremely wealthy and wanted to establish relations with Han, but had been unable to do so. Upon meeting Zhang Qian, he was very pleased and asked where he intended to go. Zhang Qian replied: "I was sent by the Han court on a mission to Yuezhi, but the Xiongnu blocked the route. Now I have escaped from them and come here. I hope Your Majesty will send guides to lead me to Yuezhi. If I can reach there, upon my return to Han, the Han court will present you with countless treasures." The king of Dayuan followed Zhang Qian's request, providing him with guides and interpreters, escorting him all the way to Kangju, which then sent him on to Yuezhi.
It turned out that after suffering attacks from the Xiongnu, the Yuezhi king had been killed, and the majority of the people had migrated westward to this place, becoming known as the Great Yuezhi. The people had already installed the murdered king's crown prince as their new king, and they had settled down, ruling over the pre-existing kingdom of Daxia. The land there was fertile, the produce abundant, and free from external invasions. They merely wished for peace and tranquility, a carefree and happy life, and feeling far removed from the Han dynasty, no longer harbored any desire to retaliate against the Xiongnu.
Zhang Qian traveled from Great Yuezhi to Daxia but ultimately could not obtain a clear stance from the Yuezhi regarding joining forces with Han to attack the Xiongnu. After staying there for over a year, he set out on his journey back to Han.