I love the certainty that comes with performing a rehearsed show and also the uncertainty that comes with live theatre. I remember when I was performing in the National Tour of CATS, in the opening song, a huge boot is supposed to fall from the ceiling. When the boot falls, we all stop and stare at it and my character (Jennyanydots) picks up the boot and carries it offstage and then the music and dancing continue. Well, one night, the boot didn't fall, but the mechanism that was supposed to unlatch it was already released, which meant that the boot could fall at any given moment, which as you can imagine, could be quite dangerous. So the entire show had to be stopped. All of the actors were told to exit the stage (as cats, of course) and wait as the crew climbed a ladder to manually take down the boot. Once this was done, we returned to the stage, and resumed the show from where we left off. We had a lot of mishaps during the show from microphones not working to wigs coming off onstage to Grizabella getting stuck in the "heavyside layer" until the entire audience had left the theatre.
Ah, the joy of live theatre.