It's no wonder why they can't relax, can't feel the joy of creating music for others (at least before the event).
Not ready to be generous. Because generosity requires an act from a different part of the brain. The one that is activated by the giving and sharing. When threatened with the imagined danger of public humiliation ("they will laugh at me"), this brain is easily overridden by our ancient defense mechanism activated by the oldest part of our brain which was quite vital when you didn't know, if you would survive the night or an encounter with a fierce animal.
But to have a recital is to be generous in the first place.
No need for stress. Wake up to the miracles instead.