Long ago, a county magistrate named Wang Lu served in what is now Anhui province. He was notoriously greedy and accepted many bribes. One of his secretaries was equally corrupt and often schemed on Wang Lu's behalf.
One day, a man came to the magistrate to lodge a formal complaint against this secretary. The secretary's crimes were strikingly similar to those Wang Lu himself had committed. Terrified, Wang Lu forgot his judicial duty. Instead of passing judgment, he wrote on the complaint: "By beating the grass, you have startled me, who am like a snake hidden beneath it!"
This story gave rise to the idiom "Beat the grass and startle the snake." Its original meaning was that punishing one person can serve as a warning to others. Today, it is commonly used to describe premature actions that alert an opponent, putting them on guard.