The first meaning of this proverb is the original meaning, however the proverbs meaning has devoloped since. This is a story about the how this proverb may have come about.

A county magistrate named Wang Lu was very greedy and took many bribes. One of his secretaries was equally corrupt, and often schemed for Wang Lu's deeds. One day a man lodged a complaint against the secretary to Wang Lu. The secretary's crimes were almost the same as the crimes the magistrate himself committed. Wang Lu was so frightened that he forgot his proper role in handling the case. Instead of issuing a judgment, he couldn't help writing these words concerning the complaint: "By stirring the grass, you have startled me who am like a snake under the grass!"

Proverb Meaning Source: