More lack of preparedness. My approach in setting exams was always that someone who actually understood the material well would find most of the exam quite ea

More lack of preparedness. My approach in setting exams was always that someone who actually understood the material well would find most of the exam quite easy - i.e. you'd be able to pass without focusing hard. Getting top marks would require deeper understanding. The basic idea here is that any student who genuinely understood the course material should definitely be able to pass even on a bad day, or a bad exam schedule, etc. If you can't meet that mark, you shouldn't advance.