'at the end of each concert his father would be the first person he spoke to and his father's first question was always "How many mistakes did you make?" '

Ouch, ouch, ouch!!! Rule #1 in how to turn somebody off is to say things like that. Encouragement is *so* important, with children and adults alike. We're all fragile and need positive strokes. Show you're sharing in the good bits and then, maybe, suggest an area which needs a little extra attention to add that final polish.