Universities generally adopt the "credit system". When you study a subject, the minimum requirement for completing the subject is "passing". Only by passing or above can you get several credits for this subject. If you fail and don't take the make-up exam, naturally you won't get the credit for the subject, which is equivalent to learning the subject for nothing. When students graduate, those who have not completed the required credits will not be able to graduate-that is, they will not get a diploma.