Here's something I didn't expect when I first became a teacher: you get more guff from students over A-minuses than you do over Ds or Fs. I would have thought that the worse the grade, the more likely you are to get guff over it. But it turns out that I get literally no guff over grades in the D-plus to solid-B range, and two to three times more guff over A-minuses than I do over failing grades.
Of course, it actually makes a lot of sense. A person who gets an F usually doesn't care about his grades--or, if they do, they know how much work it takes to earn a passing grade and they know they didn't do it. A person who gets a D thought he was going to get an F, so he's happy about he D. But a person who gets an A-minus cares about her grades and wanted to get an A. The person who gets an A-minus doesn't see it for what it is: an extremely good grade whose literal meaning is "near excellent" or some such thing. All they see is "not-A+" and they freak out.
People are weird animals.