I think it is most important for a teacher to play the pieces and studies that are being played by the student.
I definitely have a tendency to only see the blemishes of things, and see lots of things about my acting that I don't like.
If the poor overweight jogger only knew how far he had to run to work off the calories in a crust of bread he might find it better in terms of pound per mile to go to a massage parlor.

