10
The detailed reputation breakdown (available from expanding the list item by clicking on the little arrow) shows that you both got a downvote (-2) and someone revoking his earlier upvote (-5).
7
You got an unupvote (-5) as well as a downvote (-2): presumably from the same person, changing their upvote to a downvote. From your reputation history (don't click if you want to preserve that number in the top of your reputation tab):
5
The way the Stack Exchange (SE) system (that Literature, this website, is a part of) works, commenting on other people's posts is a privilege, awarded when a user reaches 50 reputation points. One of the reasons for this is keeping the comments constructive: SE is by no means a social media, and reputation is at least partly intended to be a measure of a ...
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