I've already said this:
You approach expressing yourself with certainty, not mumbling under your breath and looking away from her. Confidence is about self-belief and being certain of what you're going to say, what you're about, how you present yourself, express yourself (and to a certain extent you need to know what you're actually about otherwise you'll just come off as a bull**** artist).
Yes it's vague, it's a vague term, like many, like the previously mentioned "belief". Belief can be used interchangeably with confidence in many instances, and on top of that belief is even more ambiguous, or do you question the existence of it as well?
Now, fine if you want to reject what I'm saying, but it is as definitive and concise as you're going to get on a definition of the word. Ultimately it's about certainty.
You still haven't explained further on this "by-product of predictability" comment I've seen you write a handful of times on here, in fact I've never seen you explain it, you just say "That's IT. Period." and nobody cares enough to actually call it into question, and I didn't care enough up until now. But the irony that my and others definitions are so vague and useless yet you seem to be avoiding explaining yours any further, is it TOO vague?