Expressing Regret & Completion: 〜てしまう (shimau)｜〜てしまう
The auxiliary construction 〜てしまう (attached to the te-form of a verb) is one of the most expressive structures in Japanese. Depending on context, it conveys two distinct psychological dimensions: either an unintentional, regrettable mistake ("unfortunately ended up doing"), or the thorough, complete execution of an entire task ("finished completely"). Learning to recognize these two meanings will help you interpret conversations with natural emotional depth.
うっかりミスをして後悔したときや、あることをすっかり全部終わらせたときに『〜てしまう』を使います。気持ちのニュアンスと使い方を練習しましょう。
Accidental mistakes and regret (Unintended actions)
When combined with an accidental event or mishap, 〜てしまう expresses the speaker's frustration, regret, or embarrassment that something occurred contrary to expectations: 鍵をなくしてしまいました (I unfortunately lost my key). It emphasizes that the action was involuntary.
失敗やハプニングのときに『〜てしまいました』を使うと、『うっかりやってしまった』『とても困った・残念だ』という気持ちが伝わります。
Complete fulfillment and thorough finishing (Completion)
When combined with an intentional task, deadline, or consumption, 〜てしまう expresses that the action is brought to full completion without leaving anything behind: 今日中にこの本を読んでしまいます (I will finish reading this whole book by the end of today).
仕事や宿題、食事などを『すっかり最後まで終わらせる』ときにも『〜てしまう』を使います。
Everyday spoken contractions: 〜ちゃう and 〜じゃう
In everyday casual conversation, 〜てしまう readily contracts to 〜ちゃう (e.g. 食べちゃう, 忘れちゃった), and 〜でしまう contracts to 〜じゃう (e.g. 飲んじゃう, 読んじゃった). These forms are omnipresent in friendly chat.
友達との会話では、『〜てしまう』が『〜ちゃう』、『〜でしまう』が『〜じゃう』という親しみやすい形によく変わります。
How to tell regret from completion
Context and tone guide you immediately: negative outcomes (forgetting, dropping, arriving late) signify regret; goal-oriented tasks (writing reports, finishing meals, cleaning rooms) indicate thorough completion.
忘れ物や遅刻なら『後悔』、レポートの完成や完食なら『完了』と文脈で判断しましょう。
Examples / 例
The following scenes and exercises were written for this lesson. They do not describe an actual service or event.
大切な会議の時間を間違えて、遅刻してしまいました。
I unfortunately mistook the time of the important meeting and arrived late.
Expressing regret over an unintended scheduling blunder.
今日の午後までに、この報告書を全部書いてしまいます。
I will completely write up this entire report by this afternoon.
Expressing determination to finish an entire task thoroughly.
自転車の鍵を道に落としてしまって、とても困りました。
I accidentally dropped my bicycle key on the street and was in big trouble.
An unfortunate everyday mishap involving lost property.
とてもおいしい料理だったので、全部残さず食べてしまいました。
Because the food was so delicious, I completely ate every bit without leaving anything.
Complete finishing of a delicious meal.
Practice / 練習
Read each situation. Say your answer before opening “Answer and explanation.”
Q1. You regret oversleeping on the morning of an important test: テストの日の朝に（寝坊してしまいました／寝坊するつもりです）。
Answer and explanation
寝坊してしまいました
An accidental, regrettable blunder is expressed with 〜てしまいました.
Q2. What is the casual spoken contraction of 飲んでしまいました: （飲んじゃいました／飲んじゃう／飲みました）。
Answer and explanation
飲んじゃいました
The te-form 飲んで plus しまいました contracts conversationally to 飲んじゃいました.
Q3. Does "今月のお小遣いを全部使ってしまった" convey regret or pure completion?
Answer and explanation
後悔
Spending all your allowance is a regrettable loss/mistake, conveying remorse.
Q4. Correct the verb ending for a past accident: "昨日、電車に傘を忘れてしまいます".
Answer and explanation
忘れてしまいました
Past accidents require the past polite form 忘れてしまいました.
Words / 言葉
| Japanese | English |
|---|---|
| 失敗 | failure; mistake |
| 後悔 | regret; remorse |
| 完了 | completion; conclusion |
| 報告書 | written report |
| 不注意 | carelessness; oversight |
A phrase to use
すみません、間違えて別のボタンを押してしまいました。
I am sorry, I accidentally pressed the wrong button.
Sources
Grammar reference: The Japan Foundation, Irodori: Japanese for Life in Japan. The explanations here are concise original summaries; examples and practice questions are original.
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