가슴에 못을 박다

The phrase literally translates to 'to drive a nail into one's chest'. '가슴' (gaseum) means 'chest' or 'heart', and '못을 박다' (moseul bakda) means 'to drive a nail'. This idiom vividly describes the act of causing deep emotional wounds, likening the pain to having a nail hammered into one's heart. It implies a lasting and sharp pain, as a nail, once driven, is difficult to remove and leaves a mark.