从前楚国有个贵族，祭祖之后，赏给前来帮忙的人一壶酒，这些人互相商量着说：“这壶酒大家都来喝则不够，一个人喝则有余，这样吧，让我们各自在地上画一条蛇，谁先画好，谁则喝这壶酒。” 其中一个人最先把蛇画好了。他端起酒壶准备饮酒，发现别人还在埋头苦干，于是他便得意洋洋的左手拿着酒壶，右手继续画蛇，他说：“我还能够给它添上脚呢！”没等他画完，另一个人已经把蛇画成了，那个人把酒壶抢了过去说：“蛇本来没有脚的，你怎么能给它添上脚呢？”于是就把壶中的酒喝了下去。 这个给蛇添脚的人虽然先画好了，却最终失去到手的那壶酒。

     蛇本来没有脚，先画成蛇的人，却将蛇添了脚，结果不成为蛇。后遂用画蛇添足，比喻节外生枝，多此一举，反而坏事。人们做任何事都要实事求是，不卖弄聪明，否则非但不能把事情做好，反而会把事情弄砸。

画蛇添足英文版
      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 enought wine for all of them, and decided to each draw a picture of 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?"

      This idiom refers to ruining a venture by doing unnecessary and surplus things.