Good question, OP. The thing is, if you're insecure, you will over qualify yourself, over share, etc. I've had this problem, although it things varies depending on context. Changing "external" behaviour like suggested in above posts can change your internals, yes.
It's also about abundance mentality. I had a conversation with a girl on a train yesterday, and I took a break and stared out the window, and she reciprocated/took initiative. It's the same thing as with to maintain mystery, to be "rich" to the degree of being able to always let go. I think one should qualify oneself as little as is needed, she should drive it as much as possible. I got a way to go here, still.