In the Spring and Autumn Period (chūn qiū shí qī  春秋時期,770-476 BC) ,there was an expert archer in the State of Chu (chǔ guó 楚國) called Yang Youji (yáng yóu jī 養由基). To test his skill, someone chose three leaves at different heights on a willow tree, and challenged him to hit them in order. Yang Youji stood more than one hundred paces away, and hit the three leaves in order.

This idiom describes excellent marksmanship. Later it became used to indicate great and assurance.

中國古時候有一個人叫養由基，他射箭的技術非常好。有人在樹上掛了三片樹葉，并寫上1、2、3，讓養由基來射。養由基站在100步以外的地方，拉開弓，搭上箭，第一箭射中了第一片葉子，第二箭射中了第二片葉子，第三箭射中了第三片葉子。

這個成語本義是形容射箭技術高超，每次都能命中目標。常常用來比喻做事有充分的把握，總能達到預期的目的。

百發百中 (bǎi fā bǎi zhòng)
【翻譯】every shot hits the target.
【釋義】形容射箭或打槍準確，每次都命中目標。也比喻做事有充分把握。
【例句】這么多問題你都回答對了，真是百發百中。
【近義詞】彈無虛發、百步穿楊、百無一失
【反義詞】無的放矢、百不一存