In the Warring States Period, Duke Wei of Qi neglected state affairs, for the first three years of his reign, giving himself over to dissipation. One of his ministers, Chun Yukun who had a good sense of humour, said to him: 'There is a big bird which has neither taken wing nor sung for three years.' The duke answered, 'Once that bird starts to fly and sing, it will astonish the world.' The duke thereupon devoted himself to his duties and built his state up into a powerful one.
“一鸣惊人”用来表示平时默默无闻，一旦行动起来，却做出惊人的成绩。
This idiom is used to indicate that a person may rise from obscurity and achieve GREatness.
