A memory from an orchestra rehearsal years ago: The conductor, displeased with the way the ensemble sounded, told the orchestra, "You're only as good as your most recent performance. Remember that! (When) it's garbage, you're garbage!"
Another memory of a different conductor, leading another ensemble whose rehearsal hadn't gone well: At the end of a rehearsal, he told the orchestra, "Next week's rehearsal is going to be prepared, and it's going to be professional. If it isn't, I'm going to kick some butts!"
Strangely enough, in both cases, the next rehearsals sounded better. Fortunately, no one was kicked, either. I could just imagine the next concert programs reading, "Thanks to the conductor's exasperated threats, the orchestra will present an inspired performance tonight of..."