During the reign of Emperor Wu of the Western Han Dynasty, the Xiongnu and Yuezhi tribes in the northwest were at war, and the Yuezhi were defeated, fleeing westward. The Xiongnu frequently raided Han borders, so Emperor Wu sent the court official Zhang Qian as an envoy to the Western Regions to establish friendly relations with the Yuezhi and form an alliance against the Xiongnu.
Zhang Qian, along with his attendants, set out on a diplomatic mission to the Yuezhi in the Western Regions. However, while passing through territory controlled by the Xiongnu, they were captured by a Xiongnu patrol and taken before the Xiongnu Chanyu.
The Xiongnu Chanyu detained Zhang Qian and his party, saying, "The Yuezhi are to our northwest—how can you Han people send an envoy there? If we wanted to send an envoy to the Yue Kingdom (present-day Guangdong and Guangxi), would you let us go?"
Zhang Qian was detained by the Xiongnu for over a decade. The Xiongnu chanyu gave him a wife and children, but though outwardly compliant, Zhang Qian never forgot Emperor Wu of Han's mission.
Over time, the Xiongnu gradually relaxed their watch over Zhang Qian. Seizing the opportunity, Zhang Qian and his attendants escaped. They traveled northwest for dozens of days, arriving at the Kingdom of Dayuan. The king of Dayuan, astonished to learn they were envoys from the Han Dynasty, had long heard of Han's great wealth and desired friendly relations. After inquiring about Zhang Qian's mission to the Yuezhi Kingdom, the king provided guides and interpreters, sending them to the Kingdom of Kangju, where the Kangju king arranged further escort to the Yuezhi Kingdom.
By this time, the Yuezhi kingdom had already migrated westward to the former site of the Daxia kingdom, settling there in peace. The land was fertile and abundant, free from foreign invasion, and the people lived contentedly. The Yuezhi Chanyu, feeling that their new homeland was now far removed from the Han dynasty, no longer wished to join forces with Han to fight the Xiongnu.
Zhang Qian spent a year in the Yuezhi kingdom, repeatedly urging their chieftain with heartfelt arguments about the benefits of joining the Han Dynasty to fight the Xiongnu. Yet each time, the chieftain gave evasive replies, never making a commitment. Frustrated, Zhang Qian had no choice but to return home. Though he failed to secure an alliance, his epic journey to the Western Regions blazed a trail that would shine forever in history.
Later, the idiom "cannot grasp the main point" is generally used to describe speaking or writing that fails to capture the key or essential point.
Source: *Records of the Grand Historian*, "Biography of Dayuan"
Meaning of the Idiom: Later, the Chinese idiom "不得要领" came to describe how speaking or writing fails to capture the key or essential point.