I would say in regard to social anxiety, the reality is you can overcome it, and thus it isn't a belief at all. Destroying lies about why you should be anxious might help.

I have social anxiety (and I'm in sales). One trick I've learned is this: People don't give a shit about you when you walk in a room. They aren't judging you nearly as much as you think they are. They don't care if you flub a sentence or drop your portfolio. They won't remember the negative aspects of your interactions. Just be nice. Smile. Don't try to do too much.

This trick is to counter the feeling that many with social anxiety have that others are actively judging their words and actions. It's just not true.