一鸣惊人

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（浪费，损耗） . 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（使惊讶） the world.' The duke thereupon（于是，随即） devoted himself to his duties and built his state up into a powerful one.

This idiom is used to indicate that a person may rise from obscurity（朦胧，阴暗） and achieve greatness.