That was the one-sentence lesson, rather blunt and probably offensive, but in the end, very helpful. Often, what's needed most is a shocking jolt of reality, rather than repeated flattery.
Sounding great starts well before the first note of the day. A strong musical concept must motivate every phrase. Today's determination: nothing is going to sound bad! It's all going to be good, right?
A great musician warms up like everyone else, except that he/she always sounds amazing! Etudes, recitals, solos and excerpts likewise. It's not up to luck, however. The great sound is the result of an obsessive striving for control and style. There must be a daily pursuit of a great sound.
Mediocrity is a terrible goal. No one pays to listen to average boring playing ever. Great musicianship matters in the practice room. Great musicianship is expected on the stage and demanded by the audience.