One day, the great historian and writer Sima Qian sat in his study, feeling deeply disheartened and unable to focus on writing his *Records of the Grand Historian*.
It turned out that he had heard Li Ling was defeated, captured, and surrendered to the Xiongnu. This Li Ling was the grandson of the famous Han general Li Guang and served in the same court; though they had little interaction, he admired his character, considering him a "remarkable man" who was filial, trustworthy, incorruptible, modest, and prudent.
"Someone like him—how could he ever become a surrendered general?" Sima Qian simply could not believe it, and he decided to uncover the truth.
After investigating, Sima Qian discovered that Li Ling's surrender to the Xiongnu was not without cause. Emperor Wu of Han had ordered his brother-in-law, General Li Guangli, to lead the main campaign against the Xiongnu, with Li Ling assigned to assist. While Li Guangli advanced toward the Qilian Mountains, Li Ling took 5,000 infantry on a separate route to divide the enemy's forces. He was soon surrounded by 80,000 enemy troops. Despite fighting fiercely, his arrows ran out and supplies were exhausted, leaving no path forward or back—yet Li Guangli refused to send reinforcements. Li Ling's surrender, Sima Qian argued, was partly the fault of the emperor's own brother-in-law.
Sima Qian thought to himself, "Li Ling's surrender was most likely a feigned one, intended to bide his time and later repay the court. Even if not, his past military exploits should be enough to offset his crime. Yet Emperor Wu executed his entire family—that is far too cruel. I must find an opportunity to speak to the emperor about this."
A few days later, Emperor Wu of Han summoned Sima Qian to discuss state affairs, and the historian bluntly shared his views on Li Ling's surrender. Still seething with rage, the emperor heard Sima Qian defend Li Ling while subtly criticizing the imperial relative Li Guangli, and flew into a fury, ordering Sima Qian to be castrated and thrown into prison.
Sima Qian never imagined disaster would strike so suddenly. In prison, he was tormented, reflecting deeply. He thought of Li Ling, who had always been loyal to the court, yet now bore the shameful label of "traitor"—how cruel reality was! He felt Emperor Wu was utterly heartless; for merely speaking a few fair words on Li Ling's behalf, he was subjected to the most humiliating punishment of castration. He realized that serving the emperor was like sleeping beside a tiger. He contemplated death, but then thought that his own death would be like losing a single hair from nine oxen, or like the death of an ant—utterly worthless! He remembered his good friend Ren An, who had once written asking about "the duty of recommending the worthy," and he had yet to reply. So, he decided to write a letter in response.
In his letter, he wrote: "...All men must die, but some deaths are weightier than Mount Tai, while others are lighter than a wild goose feather..." He expressed his indignation and explained that the reason he endured humiliation and clung to life was to write the great historical masterpiece, *Records of the Grand Historian*.
Soon after, Emperor Wu of Han felt his punishment of Sima Qian was too harsh, so he pardoned him and appointed him as the Palace Secretary, a position typically held by eunuchs.
Later, people used the idiom "Lighter Than a Swan's Feather" to describe something extremely trivial or worthless.
Source: *Book of Han*, "Biography of Sima Qian"
Meaning of the Idiom: Later, the Chinese idiom "轻于鸿毛" came to describe how something extremely trivial or worthless.