The story in Strategies of the Warring States · Anecdotes of Qi State Says：
故事出自《战国策》卷九《齐策二》，大意是说:
An official of the ancient State of Chu awarded a pot of wine to his men after the ceremony of Spring Sacrifice.
楚国有一个官员，在春天祭过了祖宗之后，便将一壶酒赏给他的手下人。
One man said，“ We have only one pot of wine.
有人提议：“我们只有一壶酒，
It’s not enough for all of us but sufficient for one.
肯定不够我们大家喝的，一人喝倒是绰绰有余。
Let's determine who'll have the wine by drawing a snake on the ground.Who finishes first will have it. ”
我们每人在地上画一条蛇，谁画得最快，就把这壶酒给他。”
The others agreed.
大家都同意了。
Very soon, one man finished his snake.
有一个人很快就把蛇画好了。
He was about to drink the wine when he saw the others were still busy drawing.
他正打算喝这壶洒时，看见别人都还忙着画呢。
He said complacently,
他就得意扬扬地说：
“How slowly you are!
“你们画得好慢呀，
I still have enough time to add feet to my snake. "
等我再画上几只脚吧！ ”
But before he finished the feet, another man finished his snake and grabbed the pot from him, saying,
他的蛇脚还没画完，另一个人已经把蛇画好了。那人把酒壶夺了过去说：
" Whoever has seen a snake with feet?
“有谁见过长脚的蛇？
Yours is not a snake，
你画的不是蛇，
so the wine should be mine!”
这壶酒应该是我的了。”
He drank the wine.
说罢，就喝起酒来。
The man adding feet to the snake had to give in and could only regret his foolishness.
那个给蛇画脚的人没办法，只能懊悔自己的愚蠢。
From that story comes the idiom “Draw a snake and add feet to it”.
“画蛇添足”这个成语就是从这个故事来的。
Now people use this idiom to illustrate the truth that going too far is as bad as not going far enough.
现在人们用它来说明这么个道理:做的过分和做的不够是一样有害的。
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