In the Spring and Autumn Period (chūn qiū shí qī  春秋时期,770-476 BC) ,there was an expert archer in the State of Chu (chǔ guó 楚国) called Yang Youji (yáng yóu jī 养由基). 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.

中国古时候有一个人叫养由基，他射箭的技术非常好。有人在树上挂了三片树叶，并写上1、2、3，让养由基来射。养由基站在100步以外的地方，拉开弓，搭上箭，第一箭射中了第一片叶子，第二箭射中了第二片叶子，第三箭射中了第三片叶子。

这个成语本义是形容射箭技术高超，每次都能命中目标。常常用来比喻做事有充分的把握，总能达到预期的目的。

百发百中 (bǎi fā bǎi zhòng)
【翻译】every shot hits the target.
【释义】形容射箭或打枪准确，每次都命中目标。也比喻做事有充分把握。
【例句】这么多问题你都回答对了，真是百发百中。
【近义词】弹无虚发、百步穿杨、百无一失
【反义词】无的放矢、百不一存