SA is always a result of past experience.
No, SA is a result of our brain's physiological make-up. I know for myself that I was very anxious from as early as I can remember. Past experiences may trigger our SA and other anxiety disorders but they are not the cause of the anxiety disorder. It is extremely unlikely that people with SA just have unique experiences that nobody else has. An example of this is PTSD. With PTSD, many people experience exactly the same events but only a certain percentage of those people develop PTSD from the event.
There is a belief behind every fear.
What we experience is anxiety. Anxiety is an emotion that has evolved so as to keep us out of danger. We have an inbuilt ability to sense dangerous situations. Social situations were important situations for human survival and so the human brain has evolved the ability to notice facial language and so on that it perceives as threatening or negative, just like it has developed the ability to notice when an animal is about to attack. These are not core beliefs, these are inbuilt mechanisms. Another example is physical attraction. Humans feel physically attracted to someone based on various human attributes such as their body shape. This isn't some kind of core belief that you can unlearn, it is part of who you are.
Often, when a person with SA is in a social situation they will feel that "something bad will happen" if they don't get out of the situation quickly. This is also not a "core belief", it is just a feeling that occurs due to the fight or flight mechanism. If a person is wired to go into flight or fight mode when they should instead just be mildy anxious, you get the dysfunctional symptoms of SA.
The fear is actually the result of beliefs.
The anxiety does not have to be a result of the beliefs. Further, beliefs are generated by our brain. Let me now give you the example of a normal person who is depressed after a series of bad experiences. The depressed person starts to think all kind of irrational things like the idea that there is no way out and so on. Give them a few days to get over the events and suddenly all of their beliefs change back to normal. As you can see, beliefs are an outcome of the brain's chemicals and processes. Another example is the effect that alcohol has on a person with SA. Suddenly all of their beliefs are different when under the influence of this drug.
Further, beliefs can develop as a result of anxiety and other stimulus such as pain. This is known as fear conditioning. For example, if you paired a foul odor with a particular room, you would start to fear that room before you even entered it. Now imagine that a person's brain becomes highly anxious in various situations, and think about how a person then learns to fear those situations.
An even more complex take on the role of beliefs in anxiety disorders can be found in OCD. With OCD, the person knows that their beliefs are irrational but due to the overwhelming emotion, they cannot convince themselves of this fact. Despite the person having all the ability to rationalise things as everybody else, they cannot do so due to the emotion. Further, these beliefs are often created at the time and the number of them can be infinite.
The ONLY fear that human beings are born with is a fear of loud noises. Every single other fear is the result of conditioning based on beliefs.
But anxiety, just like the feeling of arousal, is something that is built into humans. You cannot teach somebody to be gay for example. We are hard-wired to get anxious at certain times otherwise we would not survive. You appear to just be refering to conditioned fear. It is only an aspect of social anxiety disorder and certainly not the cause.
It's never impossible to overcome SA, but the longer we've lived with it the more "stuck in our ways" we might seem.
A person experiences physiological changes over their lifetime. Certain hormones go up and down at different stages in a person's life. SA usually arises during our younger years because evolution has probably dictated that this is an important time to be performing socially. Therefore, as you get older, you may find your symptoms decrease or go away without doing anything in particular. As the chemical levels change, so will your beliefs.
Medication can mask the symptoms, but as long as those beliefs still exist, SA will find a way rear its ugly head.
The beliefs themselves are just a symptom of SA. People do not talk of a cure because the main catalyst of SA is a lump of matter that we can only influence to a certain degree.
With social anxiety, it's EASY to play the victim. It's easy to pity ourselves. It's easy to blame past experiences, genetics, our family, our friends, and so on. It's easy to say that things are hopeless. It's easy to give up.
Things are not hopeless. People achieve a lot while still having an anxiety disorder. There are also some things that can probably help to manage the disorder.
CBT can be a huge help, but in the end, only we can change our own beliefs. We can train ourselves to recognize when we're thinking negatively/irrationally. As soon as we catch ourselves, we can focus on something else: our breathing, a song, a positive thought, anything except that negative thought. We can get better at this and start noticing negative thoughts immediately and cutting them off. The better we get, those negative thoughts will start happening less and less.
From past experience, all this has resulted in is that I have become a neurotic basketcase that is focused on the internal workings of my brain and body when that is the last thing I want to do.
By the way, what you are suggesting is just a form of avoidance. Avoidance is in itself is a major aspect of anxiety disorders and is what helps the anxiety disorder to persist. If you are in a social situation and are focused on a positive thought or some kind of neurotic internalisation, you are in fact just avoiding the situation while still being there. I think this is what triggered my OCD. You see, with OCD, you go into a situation (eg a social situation) and your brain starts to distract you with something and you start to reorganise the position of book or whatever instead of focusing on the conversation. So when I was getting this kind of therapy, I would go into the social situation and start thinking of positive thoughts and repeating them over and over again as my brain started to notice that the distraction decreased the anxiety. This is called negative reinforcement.