During Freshman Week I signed up for the Freshman Talent Show. My roommate at the time played for me, and I sang Habanera from Carmen in a jean dress, cowboy hat, and motorcycle boots. I felt comfortable with the piece since I'd performed it in festivals before, and decided I didn't need to rehearse that much.
Well, I got up there and decided I would try something new – I decided it would be a great idea to try to involve the audience somehow. At the chorus I turned the microphone to the crowd, but that threw me off and I lost my focus. My pianist stopped playing and I looked back at her during the obvious silence. Somehow, both of us picked up the song from somewhere else and finished it.
People still remember the performance favorably, but more importantly, my first relatively major failure on stage (of course I'd flubbed lines in plays before but usually had smoothed over it in character) lessened my desire to perform. Instead, I took up the other side of the table and for the next two years produced a musical, which I absolutely loved. In fact, I just applied to graduate school for arts administration to continue my newfound love after college – and get paid for it. Good thing I messed up in front of the entire freshman class the first week of college!