Back when I was 17 I played in a death/thrash band with some highschool buddies, we were pretty good, we gigged a fair amount around the city, and the only reason the school kept my drummer enrolled was because they thought the band might go somwhere.
I played lead guitar in that band, and I would get nervous before solos and sometimes tense up, I would always play the more technical, alternately picked shred type stuff, and the other guy was more bluesy and a little bit sloppy. He didnt care if he hit a few bum notes, but I was really anal about it, I'd beat myself up about it after a gig, if I was doing a fast alternate picking section over double bass drumming, my pick would ideally hit, every time the drum did, and if I messed it up, I would be so pissed.
Then it all changed one day, I lightened up about it and found my playing improved, I wasnt to intent on hitting every note dead on that the pressure wasnt on and it sounded better.
Now when I play, I don't get stressed at all, I know I can play, and I know most non musicians in the audience wont even notice mistakes anyway!