This is the 5858th most frequent Korean word.
불가능하다
To be impossible.
Here, '불가능하다' is used descriptively to indicate that the action of solving the problem cannot be accomplished.
이 문제를 해결하는 것은 불가능하다.
It is impossible to solve this problem.
In this sentence, '불가능하다' expresses the subjective impression that punctuality cannot be achieved by the subject.
그가 시간을 지키는 건 정말 불가능해 보여요.
It really seems impossible for him to be punctual.
Here, '불가능하다' is used in a past context to describe the appearance of infeasibility before an eventual success.