During the warring states period, the ruler of the Chu Kingdom 楚莊王 had been ruling for 3 years without much regard for governing.  He enjoyed hunting, drinking, and spending time with his court of concubines.

One day his doctor went to see him and came upon him holding a woman, sitting in front of a set of instruments.  The king asked, did you want to come drink, listen to music, or talk?

The doctor said, there was a huge bird, wearing many different colors, resting in our country on top of the mountain for 3 years now.  He can’t fly, doesn’t speak, what kind of bird is this?

The Chu King 莊王 knew the doctor was referring to him, said with a grin: I know, this isn’t your ordinary bird.  He hasn’t flown for 3 yrs, but once he flies he will shoot through the sky.  3 yrs without speaking, once he speaks he will surprise everyone.  Wait and see! 一鳴必定驚人

莊王 eventually did come through, slowly becoming more engaged in country affairs.  He changed government policies, trained the military, and in 6 years led the Chu nation to a strong position.  He became one of the most famous leaders in the warring states period.

When referring to people who are lurking without visibility, but once in action mode achieves very surprising things, we call that “one cry shocks all”. 一鳴驚人