Li Mi (李密) (582–619), courtesy name Xuansui (玄邃), was the leader of a rebel movement against the rule of Emperor Yang, the last monarch of Sui Dynasty.
As a young nobleman from the military family, Li Mi became a guard of Emperor Yang at the age of 16, but a short time later he was caught gazing around on duty by the Emperor, who thus told his prime minister to have Li Mi removed. The prime minister said to Li Mi:" Son, you are a man of gentle blood. You are supposed to come to the top by talent and learning. Why are you wasting your time to be a guard?"
Thinking his words were very convincing, Li Mi readily resigned from the imperial guard corps, and began to study hard. Legend has it that when he traveled around, riding a bull, he always hung his books on the bull's horns so that he could read anytime and anywhere. One day, Yang Su, an high official and the uncle of Emperor Yang, happen to see him reading on the bull-back. Surprised by Li Mi's studiousness, he took Li Mi back to his home. After talking with Li Mi, Yang Su said to his son Yang Xuan Gan, "Li Mi's intelligence and capability is far beyond yours."
Therefore, Yang Xuan Gan tried to cultivate Li Mi, and made Li Mi his heading strategist.
Background and Writer Comment:Yang Xuan Gan rebelled against Emperor Yang in 613 but failed, and Li Mi subsequently led a rebellion against Emperor Yang in his own right in 617, gaining victories at first but also failed eventually.
This Chinese idiom story is from the "New Book of Tang (新唐书)", a classic work of history about the Tang Dynasty.
The idiom of Hang Books On The Bull's Horns--Niu Jiao Gua Shu refers to lack of perseverance.