Students sometimes ask me how to balance demanding perfection in the practice room with accepting the inevitable mistakes that happen in performance. If we forgive ourselves for making mistakes, doesn't that lead to complacency?
Remember that performance relies entirely on the integrity of the preparation. Practice Monster is a necessary part of that process, but he has no place on the stage. I have a cartoon on my studio door that shows a young student asking his teacher, "If practice makes perfect, and nobody's perfect, does that mean nobody is practicing?" Of course not! But if we can wrap our heads around the deep meaning of that little newspaper comic, we see the practice/performance paradox.
Never tolerate mistakes in your practice. Stay organized and on task, and let Practice Monster occasionally fuel the fire that keeps you coming back for more. Prepare with ferocious tenacity, intensely focussing on the tiny little details. When the time comes to perform, soften your focus to the see the whole process. Be the friendly Performance Monster, sharing the ultimate expression of your work with the audience. Don't worry about mistakes! If you have spent enough time and energy preparing, the performance will be the best that you can offer, and that's all that matters.
Be critical at the appropriate times, especially as you prepare, and as you eventually evaluate the final result, but don't rob yourself of the joyfulness that we can experience on the stage. There is nothing like the feeling of a fun performance, and if you enjoy yourself and shrug off the mistakes, your audience will have fun too!