success on the first try; hitting the target with one shot
A yojijukugo emphasizing achieving a goal or hitting a target in a single attempt. Often used figuratively for immediate success.
He passed the difficult exam on his first try.
Aiming to hit the target with one shot, he carefully released the arrow.
一発 means 'one shot' or 'one attempt', while 一発必中 adds the nuance of certain success in that single attempt.
百発百中 means 'every shot hits the target' (100 out of 100), implying consistent accuracy, whereas 一発必中 focuses on succeeding in a single decisive attempt.
A yojijukugo composed of 一発 (one shot) and 必中 (certain hit). The exact historical origin is uncertain, but it follows a common four-character idiom pattern emphasizing decisive success.