〜ずにはすまない
Formation
Meaning
Indicates that one must perform a certain action due to the circumstances, social common sense, or feelings of obligation. It implies that failing to do so would be unacceptable or unforgivable.
Note
A formal and literary expression. It implies a strong sense of social or moral obligation. Failing to do so would be considered unacceptable, either by the subject themselves or by society. Often used when taking responsibility for an action.
Examples
これだけの損害を与えたのだから、謝らずにはすまない。
Since I've caused this much damage, I must apologize.
警察に知られた以上、本当のことを話さずにはすまないだろう。
Now that the police know, it will likely be necessary to tell the truth.
多くの人に迷惑をかけたのだから、辞任せずにはすまなかった。
Because I caused trouble for many people, I had no choice but to resign.
大切な書類を紛失して、謝罪せずには済まない事態になった。
Losing the important documents became a situation where an apology was unavoidable.
このまま問題を解決しないではすまないことは分かっている。
I understand that I must resolve this problem eventually.
多くの人に迷惑をかけた以上、謝罪しないではすまないだろう。
Since I've caused trouble for so many people, I must apologize.