In the Warring States Period, a man in the State of Chu was offering a sacrifice to his ancestors. After the ceremony, the man gave a beaker of wine to his servants. The servants thought that there was not enough wine for all them, and decided to each draw a picture of a snake; the one who finished the picture first would get the wine. One of them drew very rapidly. Seeing that the others were still busy drawing, he added feet to the snake. At this moment another man finished, snatched the beaker and drank the wine, saying, 'A snake doesn't have feet. How can you add feet to a snake? '
“画蛇添足”这个成语比喻做了多余而不恰当的事，反而把事情弄糟了。
This idiom refers to ruining a venture by doing unnecessary and surplus things.
