What it means
ではすまない means that a situation cannot be resolved, excused, or considered sufficient by the preceding noun, adjective, or action alone. It often implies that a more serious response, consequence, or additional measure is required. With a verb, it commonly follows a plain-form clause with だけ, as in “merely doing X will not suffice.” The familiar ending is ではすまない, while the polite counterpart is ではすみません.
Usage note
This pattern often carries a strong sense of accountability or seriousness, so it is more forceful than simply saying that something is insufficient. Do not confuse it with では済まされない, which more explicitly means that something cannot be excused or allowed to pass.
How to use it
この損害は謝罪ではすみません。
This damage cannot be settled by an apology.
今回の処分は形式的ではすみません。
This time, the disciplinary action cannot be merely formal.
この不正は担当者を処分するだけではすみません。
This misconduct cannot be resolved by merely disciplining the person in charge.
この損害は謝罪ではすまない。
This damage cannot be settled by an apology.
今回の処分は形式的ではすまない。
This time, the disciplinary action cannot be merely formal.
この不正は担当者を処分するだけではすまない。
This misconduct cannot be resolved by merely disciplining the person in charge.