N.G.
If their personal best is a 100, and they got a 93, then that is a shortfall.
If their personal best is a 90, and they got a 93, that is excellence!
It is so very subjective. This never has and never will be a one-size-fits-all answer.
Case and point. I am fully capable of getting straight As and always did in school. College was no different. When I applied myself, I got perfect grades. It didn't take a ridiculous amount of effort- if I studied the same as everyone else, I got perfect grades. I just learn more easily and happen to be a great test taker. So, if I got less than perfect, I did beat myself up because I know I could have done more.
My husband, however, has never been a model student and happens to be a terrible test taker. He is very intelligent but the grades are a bit harder for him to get perfect. Bs and Cs are perfectly acceptable for him. If he gets an A, it's a major achievement.
This kid knows what he/she is capable of, and so does his/her family. If he/she was more than capable of getting a 100, then a 93 is a disappointment to them. You might find that unrealistic, but only they know what their personal best is. You can't change that.