Musicians know that every performance they play is an audition for their next engagement.
Musicians prepare for every rehearsal and performance. Conductors study their scores, decide which parts of the music to emphasize at each moment, and practice giving signals or “cues” to musicians.
Musicians learn their parts on their own time before ever walking into a rehearsal.
Musicians never stop improving their skills. Professionals continue to take lessons throughout their careers.
Professional musicians regret their mistakes, but learn from them, too, and look ahead to the next performance, the next opportunity to play well.
If a musician accepts a playing engagement, he has promised to play at a professional level. If he does not achieve that level, a real professional doesn’t blame anyone other than himself.