why does てしまう sometimes sound sad and sometimes just... done?

Question

I keep seeing 食べてしまった used for 'I accidentally ate it all' but also for situations that just sound like plain completion, no regret at all. Is てしまう always about mistakes/regret, or is there another use I'm missing?

mizu_ba55e901 · Accepted Answer

The core meaning taught at N4 is exactly what you said — unintentional action or a regrettable outcome, 'to end up doing

Answer

The core meaning taught at N4 is exactly what you said — unintentional action or a regrettable outcome, 'to end up doing' / 'to accidentally do'. 宿題を忘れてしまいました = 'I ended up forgetting my homework' (oops). If a sentence with てしまう doesn't sound sad to you, it's probably still framing something as unintended or out of the speaker's control, just less dramatically than 'accidentally' suggests in English.

Answer

Yeah, I'd just anchor on 'ended up doing X' as the safe translation every time — it covers both the guilty feeling and the milder 'well, that happened' feeling without you having to guess which one it is.

Answer

This helps, thanks. I was overthinking it as two totally separate grammar points.