Charm is almost entirely a matter of where somebody is looking. The most magnetic person at any gathering is rarely the funniest; it is the one who asks a second question, having genuinely listened to the answer to the first. That is a learnable behaviour and it has very little to do with confidence.
Nervous people are often excellent at it, because they would far rather be asking than talking. Beauty behaves less predictably than that, but it obeys some of the same rules. Faces are more interesting when they are interested in something.