what happens if you fail a subject?

hey guys. obviously not going super well here. am wondering what would happen if i fail a subject. on the unimelb page under "assessing why you failed" ( https://students.unimelb.edu.au/your-course/manage-your-course/planning-your-course-and-subjects/failing-a-subject#assessing-why-you-failed ) it says "eligible circumstances." what does that mean? if i failed a subject becuase of extraneous circumstances does that change the impact of it??

also, i want get into post graduate, even though im struggling right now. if i fail does that end my chances? any advice is appreciated!! :)