That's difficult to answer. I'm sure not everyone has public speaking or performance anxiety for the same reasons. I just try to take the consequences out of the equation. I am speaking in front of people because I have information to share or a performance to deliver. I know the material very well. It does not matter so much how I say it, my audience does not have a copy of my dialogue. If I make a mistake, who will really know? If I stumble, for all they're aware, it's part of the presentation.
I take the audience's opinion out of the equation. I pretend I'm not even speaking in front of people and I never make eye-contact.
I take the idea of a perfect presentation out of the equation. I'm just human after all.
All that's left is trying to deliver the most honest performance I can.
The time to judge myself ended once I got up on the stage.