ずにはすまない
zu ni wa sumanai
must; have no choice but to
[Must; have no choice but to; cannot get by without doing]
Connection: Verb (nai-stem) + ずにはすまない (する → せずにはすまない)
Usage: Expresses that due to social norms, moral obligation, or circumstances, one has no choice but to do something. It implies that not doing it would be unacceptable or that the situation demands action. More formal than なければならない.
Key nuance: The compulsion comes from social/moral pressure or the nature of the situation, not personal desire.
Examples:
これだけの被害を出した以上、責任者は辞任せずにはすまないだろう。(Given the extent of the damage, the person in charge will have no choice but to resign.)
人のものを壊したのだから、弁償せずにはすまない。(Since I broke someone's property, I have no choice but to compensate.)
この問題を放置すれば、いずれ対処せずにはすまなくなる。(If this problem is left unattended, we will eventually have no choice but to deal with it.)