The pianist came out on stage, bowed to the audience, sat down at his piano, and for the next two hours put on what he thought was a brilliant show.
At the end of the performance the entire audience rose up and gave the pianist a very enthusiastic standing ovation. Suddenly the pianist covered his eyes with his hands and proceeded to break down and weep uncontrollably.
The manager of the auditorium rushed up to him and begged him to tell him what was the matter. Why was he weeping and why was he so very sad.
Between sobs the heart broken pianist said that his performance was terrible, and that it had to be his worst night of playing ever. That he had no right to ever play the piano again.
The manager exclaimed, "That's ridiculous"! Just look at the people, they are all standing and applauding like crazy. You should be ecstatic.
The pianist pointed to a single man in the middle of the very first row who was still sitting down and not applauding, and who had a look of utter disdain and contempt on his face.
"He's not standing and he's not applauding", said the pianist.
The manager looked at the only man in the entire audience that was not standing and he said, forget about him. He's only one guy. He doesn't matter anyway.
And the pianist sobbing even harder said, I know, but he's my teacher.