to completely do something
This grammar implies doing something completely or irreversibly.
예문
資料をなくしてしまいました。
I lost the documents completely.
注射を打ってしまいます。
I will give the injection completely.
薬を飲んでしまった。
I ended up taking the medicine.
빠른 확인
약을 다 마셔버렸다.