GRAMMAR DETAIL

てしまう

to finish doing · to end up doing

Expresses either the completion of an action or regret over an unintended result.

Examples

たくさんの宿題を夕食の前に全部終えてしまった。

I finished all that homework before dinner.

大切な家の鍵を電車でなくしてしまった。

I ended up losing my important house key on the train.

Structure: Add しまう to a verb's て form to express completion or a feeling about an unexpected result.
Basic usage: 大切な家の鍵を電車でなくしてしまった。 conveys regret about losing a key.

Completion and regret
- 宿題を終えてしまった emphasizes finishing all the homework, while 鍵をなくしてしまった emphasizes an unwanted result. The feeling conveyed by てしまう depends on the action and context.
Conversational forms and tense
- Contractions include 買ってしまう→買っちゃう and 飲んでしまう→飲んじゃう. Their past forms are 買っちゃった and 飲んじゃった, so the tense distinction remains.