A single hair against nine oxes, is a Chinese idiom describing something that is very unconsequential, or unimportant as compared to the whole. The idiom comes from the story of Sima Qian, a very important historian in the Western Han Dynasty in the 200 B.C.

Sima Qian was born in 145 B.C. to a family of historiographers. His father, Sima Tan was a historian too for Emperor Han Wudi. As a young man, Sima Qian travelled the country to study the historical sites and looking for records of important historical figures of the past. Later he himself became an attendant to Emperor Wudi.

In 99 B.C.,Sima Qian got involved in the Li Ling Affair. During this time, the Han Dynasty was in war with the Xiongnu tribes in the North. Li Ling was one of two military officers leading a campaign against the Xiongnu. At first he won some battles, but in one battle, he was defeated by a large number of enemies and were held captive. Emperor Han Wudi attributed the defeat to Li Ling.

While all the officials in the government condemned Li Ling for the defeat, Sima Qian was the only person who defended Li Ling.He argued Li Ling's 5,000 soldiers has fought the 80,000 strong Xiongnu cavalry for 8 days and Li Ling was taken captive until all his soldiers died when their food and arrows were finished. This angered the emperor enormously. 

Subsequently, he was put to prision and was given the most humiliating punishment. He thought of committing suicide but felt his death under the circumstances would be unconsequential; just like a single hair as against the whole from nine oxes. He decided to live with humiliation and finish the recount of history that he was working on. He put this thoughts into a letter to one of his close friends, from this letter, comes the idiom, "a single hair as against nine oxes".

So he continued to write Shiji, which was finally accomplished in 91 B.C.. It has since become one of the most important works on ancient Chinese history.