Damned good question. I have no answer. Someone once told me to picture the audience naked. I tried that but it just got me all excited.
I think everyone faces stage fright at times. I recall puking before a performance many years back and I'd been in front of audiences ranging in size from tens to tens of thousands. Some folks have said, "Know your stuff." Excellent advice. Then you can go on 'auto pilot' if you feel the beast creeping up on you.