During the Spring and Autumn period, a scholar named Mr. Dongguo was traveling to Zhongshan with a large sack of books on his donkey. As he walked, dust rose ahead and a panicked wolf rushed toward him, pleading, "Sir, you must be a man who delights in helping those in distress. Long ago, a man named Mao Bao bought a turtle and set it free; later, when he fled into a river during battle, the turtle repaid him by carrying him across. Another man, Sui Hou, healed a snake's wound, and the snake brought him a luminous pearl in gratitude. Now I am being hunted by archers. If you hide me in your book sack to save my life, I will surely repay you like the turtle and snake did."
Mr. Dongguo, soft-hearted and unable to refuse, emptied his book bag and stuffed the wolf inside. Moments later, the hunter arrived and asked if he had seen a wolf. Mr. Dongguo replied, "No, I haven't," and tricked the hunter into leaving.
After the hunter had gone far away, Mr. Dongguo released the wolf from the sack. To his surprise, the wolf showed a ferocious face and roared, "Sir, you saved me just now, and I am grateful. But if you save someone, you must save them completely. Now I am extremely hungry—let me eat you!"
With that, the wolf lunged at Mr. Dongguo. Furious, Mr. Dongguo cursed the treacherous beast.
At this critical moment, a farmer arrived. After learning what had happened, he tricked the wolf back into the sack and killed it, then said to Mr. Dongguo, "Sir, a wolf's nature to eat humans will never change. Never again do such a foolish thing as saving a vicious wolf."
Later, the idiom "barely keeping alive" is used to describe struggling to maintain a thread of life.
Source: *The Legend of Zhongshan Wolf* by Ma Zhongxi (Ming Dynasty)
Meaning of the Idiom: Later, the Chinese idiom "苟延残喘" came to describe struggling to maintain a thread of life.