ないではすまない

ないではすまない is used to express that a certain action is unavoidable, mainly due to social, moral, or situational pressure.

The speaker feels that not doing the action would be unacceptable, and that they must act to resolve a situation, take responsibility, or respond appropriately.

It is very close in meaning to ずにはすまない, but ないではすまない sounds:

• slightly softer

• a bit more spoken

• less stiff than ずにはすまない

This grammar appears in both spoken and written Japanese