A certain degree of social anxiety is completely normal--even helpful. The fear of rejection or negative judgment is evolutionary: In caveperson days, rejection could mean ostracization from the pack--which meant little chance for survival or procreation. But there's a difference between wanting to be accepted, and fearing rejection so much we avoid any setting where there's a possibility of judgment (which, masochistically, is usually our own judgment toward ourselves, not someone else's).
