～てしまう
regret or thorough completion
～てしまう is made by taking the て-form of a verb and adding しまう. It adds one of two feelings to the action: it happened and you regret it or did not intend it, or it was carried out completely, to the end.
For English speakers, the regret meaning feels like “went and did” or “accidentally / unfortunately did”, and the completion meaning feels like “finished doing”.
1. Regret or accident
Use ～てしまう when something happened that you did not mean to do, or that you wish had not happened.
宿題を忘れてしまった。
“I went and forgot my homework.”
- 宿題（しゅくだい）= homework
- を = object marker
- 忘れてしまった（わすれてしまった）= went and forgot
2. Thorough completion
～てしまう can also simply mean that an action was completely finished, with nothing left over.
本を全部読んでしまいました。
“I finished reading the whole book.”
- 本（ほん）= book
- を = object marker
- 全部（ぜんぶ）= all / the whole thing
- 読んでしまいました（よんでしまいました）= finished reading
How to form it
Verb て-form + しまう
- 忘れる（わすれる）= to forget → 忘れてしまう（わすれてしまう）= accidentally forget
- 読む（よむ）= to read → 読んでしまう（よんでしまう）= finish reading
- 食べる（たべる）= to eat → 食べてしまう（たべてしまう）= eat (it) all up
In casual speech, ～てしまう shrinks to ～ちゃう and ～でしまう shrinks to ～じゃう: 忘れてしまった → 忘れちゃった, 読んでしまった → 読んじゃった.
Key idea
～てしまう means the action went all the way to the end. Sometimes that is satisfying (“finished it!”), and sometimes it is too late to undo (“oops, I went and did it”). Context and tone tell you which.
Other N4 grammar
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