The discussion on a SDaedalus thread included descriptions of dances for teenagers. The description of young men on one side, young women on the other, with few crossing over the gulf, caused me to ponder what a curse shyness is.
I am not sure what causes shyness. I suspect the nervousness of shyness comes from similar physiology to introversion. Introverts tend to have stronger startle responses and greater reaction to a drop of lemon on the tongue (they produce more saliva). However, not all introverts are shy, and some extraverts are. Most likely it is, at least partly, hereditary but there is probably more to it than bad luck at genetic roulette.
If shyness is a fear response to social situations, then what causes that? It would appear to be a phobia in that it is not a completely rational fear. At some level, for evolutionary reasons, social rejection could be a legitimate fear (loss of group protection would have been dangerous in earlier times) but I am not sure that is it (although it may be a partial explanation for the equally ridiculous approach anxiety).
Linking shyness to confidence only raises the question of what confidence is. Many shy people will be confident in other areas. They may express more doubts even in areas of competence but are probably not generally fearful.
It may not be that the non-shy person does not feel embarrassment but that the shy person feels it as more unpleasant. In much the same way that introverts “overreact” to a drop of lemon, perhaps they shy “overreact” to the feeling of social embarrassment. Perhaps the shy feel embarrassment so intensely that they seek to avoid even the possibility of it happening. This intensity of feeling may cause them to underrate their social acumen because they remember more vividly those occasions where they made some social misstep.
Although introversion and shyness are not the same, I suspect a strong link between the two. An introvert may feel less confident of their less used social skills; they will certainly have less practice. Because social interaction drains rather than energizes them, they will be less likely to overcome their fear through practice (most social situations do not end in grave embarrassment or social shame).
I do not know what causes shyness but would love to see its total eradication. For a woman it is debilitating but for a man it is devastating. It is true that practice is a good cure, but that can take a long time and may leave a long lasting (perhaps permanent) loss of overall confidence. The young men and women lining their respective walls at the dancehall would have had far more fun if they were not cursed with shyness.
While there may have once been a survival advantage to such over-caution, in the modern world shyness is grossly maladaptive. Although worse for a man, it is a detriment to both men and women. Shyness for a woman may mask her interest in a man; the averted gaze and subdued response may discourage the advance of a man she would be interested in.