A mediocre A grade?

I remember an elementary school teacher who used to rubber stamp students' papers with angels.  The message on each imprint was based ostensibly on a student's grade.  I was incensed when a test on which I'd scored 95% had an angel stamp that read, "You can do better.  I know you can."  I don't remember the subject of the test, but I still remember how it felt to see, "You can do better..." placed incongruously next to such a high score.  I fought the urge to tell the teacher sarcastically, "Sorry that my A grade fell short of your expectations..."