Guaranteed success on the first attempt; a sure hit with a single try.
あの投手は一発必中のストレートを持っていると言われている。
That pitcher is said to have a fastball that can hit the target in one go.
現実には一発必中は難しいので、継続的な努力が必要だ。
In reality, guaranteed success in one try is difficult, so continuous effort is required.