"Oh my, it's been 10 minutes and he hasn't made any mistakes yet. Time to push him over the limit. Let's all start sneezing and coughing."
"Hey Mr Sexton, could you please walk down the nave again and check with your big bundle of keys, if those chapel doors are all firmly locked? Perhaps that will help him lose focus."
If you're thinking, "what's the big deal? I've been playing for 90 minutes straight and I'm seem to be OK. It'll be just a small encore," you've already lost. You need to get out of there before your audience defeats you.
Have you ever seen the remains of an old organist by the old organs? That's the guy who didn't make it.