I'm with Ancient Mariner on this.
One of the best gigs i ever attended was the Manic Street Preachers at the NEC on the Forever Delayed tour. I wasn't a big fan of the band beforehand but walked out after show thoroughly blown away. Yet midway through the set James Dean Bradfield, an artist I now admire greatly, messed up the intro to one of the songs three times. It didn't matter. They eventually nailed and still put on a great show. I suspect Bradfield was embarrassed but nobody minded; The audience loved the fallibility and the spontaneity and I can no longer remember which song they got wrong.
Ultimately, the reason for playing live is to please the audience. Otherwise we would all just stick to the rehearsal room. I appreciate the drive for perfection and that certainly has its merits but if you entertain the punters I would say that you've achieved something more important than pure technical excellence. Of course, if you can do both then you're really cooking.