I don't think they realise how much of an impact they have on people's futures. The difference between a B and an A grade could literally be the difference between Oxbridge or no Oxbridge for people. You could argue "Well, they should've revised harder", but that isn't always the case. They could've worked hard throughout their years in education, including in the build-up to exams, but due to the fault of an examiner all their work could still leave them short of their aspirations!