How can 80% of students in a class fail a particular paper?

I'm a postgraduate student doing my masters in literature. Recently our results came out and we saw 80% of the students have failed a particular paper. It was subjective and many of them said they attempted all the compulsory questions and wrote good answers.

A small amount of students passed that paper, including me. In fact my marks in it, though not satisfactory, is far ahead of pass mark. I've also topped my university. My classmates who've failed however are making it seem like there's some mistake and I've been wrongly overestimated. I feel extremely uncomfortable and guilty.

Can anyone here tell me under what circumstances the majority of students may fail in a paper that seeks subjective answers? Thank you.

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*marks in it, though not satisfactory, are far ahead of pass mark.
How can 80% of students in a class fail a particular paper?
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