Leopold Stokowski conducted the American premier of Berg’s opera Wozzeck in 1930 (a joint effort of The Philadelphia Orchestra, the Phildelphia Grand Opera, and Curtis Institute).  Abram Chasins recalls a rehearsal:

I attended his second rehearsal with the orchestra in the pit and singers on the stage.  After some twenty minutes of singing and acting, often at sixes and sevens, Stokowski stopped the rehearsal and addressed the principle singers very quietly: “I want you all to understand something,” he said.  “Get rid of the absurd  idea that nothing in this opera matters except what you do individually, and how your voicdes sound.  Don’t you understand that you are only part of a whole dramatic entity?  You have no regard for operatic integrity.  You are vain; you want personal applause.  It is all very inartistic, and I will not put up with it.  If you can’t take this correction, just leave.”

Needless to say, no one left.

 Source: Chasins, Abram (1979) Leopold Stokowski: A Profile.  London: Robert Hale, p.130