Expresses strong will or determination to accomplish something. The 겠 marker adds a volitional/future meaning, transforming the regret nuance of -고 말다 into firm resolve.

• •Determination: "꼭 성공하고 말겠어요" (I will definitely succeed)
• •Strong will: "이번에는 해내고 말겠습니다" (I will make it happen this time)