てしまう・ちゃう

This grammar expresses that an action is completed completely, often with a sense of regret, surprise, or lack of control. It can describe actions done unintentionally or something that happened undesirably, as well as something that was completed fully. The casual contraction ちゃう is common in spoken Japanese and has the same nuance as てしまう but softer or more colloquial. Typical contexts include accidents, mistakes, or events that the speaker didn’t mean to happen, and situations where the outcome is final or irreversible. Note that insurance of regret or surprise is stronger with the しまう form, while ちゃう keeps the nuance informal. Examples: - うっかり鍵を家に忘れてしまった。 I accidentally left my keys at home. - ケーキを食べてしまった。 I ended up eating the cake (and perhaps regret it). - 財布を落としてしまって、困っている。 I ended up dropping my wallet and I’m in trouble. - 雨が降ってしまった。 It unfortunately rained (despite the plan). - 宿題をうっかり忘れてしまった。 I forgot my homework by mistake. - ついゲームをやってしまって、時間を無駄にしてしまった。 I ended up playing games and wasting time (to my regret).