Beginning with Yu the GREat, the Xia Dynasty had lasted about four hundred years before Jie became the supreme ruler.
And that was in the 18th century BC. Jie was extremely tyrannical and dissolute. This aroused GREat resentment among the people. Tang, the Chief of the tribe Shang took advantage of this situation to overthrow the Xia Dynasty and established the Shang Dynasty in the early 17th century BC. Among the preparations for the overthrow had been the winning over of popular support.
One day, Tang was having a walk in the open country. He saw a man catching birds with a big net spread in a box-like and mumbling: "Come on, birds! Come into my net. All of you, whether you are flying high or low, east or west. Come into my net!"
Tang walked over and said to the man, "This method is ruthless! You'll spare no birds this way!" With these words, he cut the net down on three sides. Then he murmured in a light voice as if praying: "Oh, birds! Fly to the left or right as you like. And if you're really tired of your life, come into this net!"
When chiefs of other tribes heard about this, they were all moved. They said, "Tang is a good king indeed. He is so kind even to birds and beasts. He must be more merciful to human beings." And very soon, about forty tribes pledged allegiance to Tang.
From that story came the idiom "Open the net on three sides". Later, people changed it into "Give the wrong-doer a way out."， indicating to be lenient to the wrong-doers.