Depends on the gig. I haven't done this in a few years, but it always seemed like a lot of it depended on the audience and on what I was expected to play. I used to get horrible--HORRIBLE--stage fright but once I got over the worst of that, of course, things improved considerably.

Beyond that, it always spoiled it if the audience turned out to be expecting something different from what we were prepared to play--one audience got quite upset because we didn't do Irish music (we were an old-time string band; we knew a little Irish music but it wasn't our focus and we didn't have anyting rehearsed well enough to play in public). Another was expecting us to sound like Nickel Creek.

On the other hand, we played weddings, etc., where people really just wanted to dance and as long as we kept playing anything at all, they were happy. We were happy.

We got hired for a Christmas outdoor pageant thing once and were all dreading the evening because none of us really knew or liked Christmas music much (but we were getting a free meal and $100 apiece). We practiced Christmas music until we couldn't stand it any more. When we got there, we got through two and a half bars of "Jingle Bells" and collectively forgot everything. Our leader shrugged and told us to start playing "Liza Jane" instead. The audience never said anything. I'm not sure they even noticed the switch and we had a much better time.