A few years ago, I started taking burlesque dance classes. A lot of the lessons concerned "how to look sexy". Which, it turns out, corresponds with a lot of behaviors people read as "confident".

I started learning how to carry myself to give the appearance of being more confident and in control. And the funny thing is that over time I started being more confident in my social interactions. Whether it was because some inner instinct was responding to me adopting confident body language, or because other people were responding to that body language and acting like I was the dominant one, I don't care. It worked. I can do something weird and crazy and people just deal with it, instead of shunning me as awkward.

Sure, if I just naturally had a confident personality then I'd have the same body language. But I feel like the causality on this is not a one-way arrow; confident personality causes confident body language, but confident body language causes confident personality, as well.