Well, Will's already said it all, so I'll just tell you about an amazing choke I recently saw...

...Lucinda Williams, main stage, Cambridge Folk Festival, five days ago. She comes on stage on her own with an acoustic guitar to rapturous applause. Mumbles some sort of introduction and starts to play. And stops. "I can't do this. I hate photographers". Puts guitar down...

And she's a top pro. So: it happens. Her coping strategy? Abandons that song, brings out the band and carries on.

I understand this is something she makes something of a habit of.

It's not a tactic I particularly commend. Best go with Will's suggestion of being well enough prepared.