Depending on the situation and the exam designer, it may well be that to "finish all the questions" is to prove oneself exceptional, at least in quickness and/or cleverness. The idea, which I don't necessarily endorse, is that it is worthwhile to give "impossible" exams, to give exceptional individuals the chance to show how far they transcend the merely-very-able, or something like that. So, instead of being a diagnostic of whether students have picked up the usual, standard ideas, such exams may pretend/aim to be detecting "geniuses". Based on observation, facility with timed exams is not a bad thing at all, but it is of limited significance in the larger scheme of things (where, for example, there is no real time limit...)
So, you have discovered that you are not ultra-fast in getting what you know onto paper. Doesn't matter much.
... tho', still, being fast is generally a good thing, if it is combined with competence. In fact, sometimes very-quick people are misled by their own successes in exams on low-level material, that is, thinking that quickness and cleverness is all there is, and not believing that the vast accumulated technique is of much significance in the face of that quickness and cleverness. (I think that is an unfortunate error of perception.)