今（いま）出（で）ないと遅（おく）れてしまうよ。

傘（かさ）を忘（わす）れてしまった。

友達（ともだち）は私（わたし）のケーキを食（た）べてしまった。

お皿（さら）が割（わ）れてしまった。

ごめん！卵（たまご）を全部（ぜんぶ）使（つか）ってしまった。

今日（きょう）は冬（ふゆ）休（やす）みの宿題（しゅくだい）を全部（ぜんぶ）してしまおう。

スノーボードに行（い）ったとき、腰（こし）を痛（いた）めてしまった。

そんな大（おお）きい声（こえ）出（だ）さないで！子供（こども）が起（お）きてしまうでしょう。

よし！誰（だれ）も食（た）べないなら、僕（ぼく）が食（た）べてしまう。

あっ、鉛筆（えんぴつ）を持（も）ってくるのを忘（わす）れてしまった。

あまりお腹（なか）が空（す）いていなかったのに、ケーキをほとんど食（た）べてしまった。

あの人（ひと）は信頼（しんらい）出来（でき）ると聞（き）いたから、言（い）ったことを全部（ぜんぶ）信（しん）じてしまった。

Using ~てしまう to express regret or completion of something

てしまう / ちゃう How To Stop Sounding Like a Robot

How to use natural Japanese: ちゃう、ちゃった

<div class='writeup-body'>By combining the conjunction particle て, with the verb しまう (sometimes written as 終（しま）う), you are able to express that something was done 'by accident', 'completely', or 'unfortunately'. These meanings may seem quite different, but we will discuss their similarities in a moment. Let's look at a few examples of てしまう first.<ul class='writeup-examples--holder'><li class='writeup-example'><div class='writeup-example--japanese'>私（わたし）はすぐに道（みち）に迷（まよ）ってしまう。</div><div class='writeup-example--english'>Unfortunately, I easily get lost.</div></li><li class='writeup-example'><div class='writeup-example--japanese'>家（いえ）にお菓子（かし）がいっぱいあると全部（ぜんぶ）食（た）べてしまうのでお菓子（かし）を買（か）わないようにしている。</div><div class='writeup-example--english'>When there are a lot of snacks in my house, I completely eat them all, so I try not to buy them.</div></li><li class='writeup-example'><div class='writeup-example--japanese'>メニューにアイスクリームがあると頼（たの）んでしまう。</div><div class='writeup-example--english'>When there is ice-cream on the menu, I unfortunately order it.</div></li><li class='writeup-example'><div class='writeup-example--japanese'>私（わたし）はよく舌（した）を噛（か）んでしまう。</div><div class='writeup-example--english'>I accidentally bite my tongue often.</div></li></ul>As we can see, verbs that usually take で instead of て will be no different when using てしまう. Sometimes, てしまう or でしまう will be shortened to a more casual form, which are often used in speech. These forms are as follows: てしまう will become ちゃう でしまう will become じゃう<ul class='writeup-examples--holder'><li class='writeup-example'><div class='writeup-example--japanese'>最近（さいきん）運動（うんどう）をしてないから太（ふと）っちゃう。</div><div class='writeup-example--english'> Recently, I haven't been exercising, so I'm totally going to get fat.</div></li><li class='writeup-example'><div class='writeup-example--japanese'>花（はな）が死（し）んじゃうから、花（はな）を踏（ふ）むな。</div><div class='writeup-example--english'>Since the flowers will unfortunately die, don't step on them.</div></li></ul><div class='writeup-funfact'><div class='funfact-header'>Fun Fact</div>While て終（しま）う is most frequently written in hiragana, て仕舞（しま）う may also be seen. There is a slight nuance difference between these two kanji structures, but the primary meaning of しまう will always be that 'something has come to the point where ending/ending up in a specific state cannot be avoided'. This 'no turning back point' may be temporary (likely to be written as 仕舞（しま）う), or it may be permanent (likely to be written as 終（しま）う). Due to this 'cannot be avoided' nuance, しまう often comes across as 'totally', as in 'ah… I totally left the chicken in the oven for too long'. In these cases, it is simply expressing the speaker's exasperation that something is 'too late' to change. However, despite regularly being used negatively, てしまう can also be used positively. In these cases it still has the nuance of 'no turning back'.<ul class='writeup-examples--holder'><li class='writeup-example'><div class='writeup-example--japanese'>ゲームを始（はじ）める前（まえ）に宿題（しゅくだい）を終（お）わらせてしまおう！</div><div class='writeup-example--english'>Let's completely finish my homework before I start playing video games! (I'm going to completely finish my homework before I start playing video games)</div></li><li class='writeup-example'><div class='writeup-example--japanese'>青木（あおき）先輩（せんぱい）、定時（ていじ）までに社長（しゃちょう）に頼（たの）まれたレポートを完成（かんせい）させてしまいましょうよ。</div><div class='writeup-example--english'>Aoki senpai, let's completely finish the report that our boss has asked us to do before work is over.</div></li></ul></div></div>

Grammar Info

～てしまう

To do something by accident, To finish completely・totally, Unfortunately