We've told this same story to students, many times over the years:
One day, you will fail.
You will be singing a funeral, and you will have a critical wardrobe malfunction, exposing all your bits to the family as well as the deceased. You will dry up on the words, forget the music, your accompanist will leave in embarrassment. It will be a disaster.
On that day, someone will come up to you and say, "Oh my Dear, that was Simply Wonderful! That was my mother's favorite song. The way you sang it was Just Beautiful. She would have loved it."
On that day, I want you to remember to smile and say, "Thank you so much! I'm glad it meant so much to you!"
Mistakes happen. Heck, lots of mistakes happen, including a bunch you didn't notice. Watch the video...
The wind will blow away your music, some toddler will knock over your music stand, someone will set off a firecracker, a dog will bark, a baby will cry, a big truck will struggle up a hill without a muffler.
You'll forget the lyrics you've sung hundreds of times, you'll forget the simplest melodies, you'll start playing in the wrong key and singing in a different wrong key.
And people will still compliment you.
Crazy right?
People aren't showing to listen saying, "I'm going to count all the mistakes." People are showing up to be entertained and to be touched in a way that only performing arts approaches.
No they aren't. They aren't saying, "That was perfect," or "Your execution of that difficult passage was the best I've ever heard." They Felt something, and are trying—necessarily imperfectly—to communicate how your performance made them feel. That can never be wrong.
Your words, your blocking, your playing, your props.
Crazy huh?
Someone's given you five minutes, or an hour, or a second of their time and you made them Feel.
That's no small thing.