Yep - my DD is disappointed with a 9, 2x7, 3A,3B - because SHE thought she could do better. (I am bloody delighted she got good grades)
We point out to her that she has done marvellously well, that her grades enable her to follow whatever future she want, she has many choices available to her - we went out for a meal last night to celebrate her achievement, but she still felt a bit down.
Her friends all had a spread of grades A* to D - but she said - "that is fine for them, I know I did better than most of them, but MY better was not good enough for ME".
Which is fair enough I suppose - if she had coasted to top results in everything, then there would be less incentive to push revision etc for A levels, now she knows she has to work harder to get to the top - which is what she strives for, she has ambition - her disappointment with good grades is just part of her.
I don't want to change her, so cannot say to her she is wrong to want to have done better , just that she does not yet realise that she has actually done blooming well.