一yī鸣míng惊jīng人rén

Literal: with a single cry, astound everyone
Figurative: To astonish everyone all at once with a great feat after a long stretch of apparent silence or obscurity.

Where does 一鸣惊人 come from?

King Wei of Qi (other versions place it under King Zhuang of Chu) had spent three years given over to pleasure, neglecting government. An adviser posed him a riddle: there is a bird that for three years neither flies nor sings—what bird is it? The king replied that once that bird took flight it would reach the heavens, and once it sang it would astonish everyone. He then set to governing and put the kingdom right.

Source (出处): 《史记》

How is 一鸣惊人 used? Two examples

他tā平píng时shí不bù声shēng不bù响xiǎng，这zhè次cì比bǐ赛sài却què一yī鸣míng惊jīng人rén，拿ná了le冠guàn军jūn。
He's usually quiet and unassuming, but in this competition he stunned everyone and took the title.
这zhè家jiā小xiǎo公gōng司sī默mò默mò研yán发fā了le五wǔ年nián，终zhōng于yú一yī鸣míng惊jīng人rén。
This small company quietly did research for five years and finally took everyone by surprise.

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