...feeling and acting confident can get you places.

Confidence is inspired by confidence. When I need to do any kind of persuasion, stating my position with confidence (not arrogance!) is so much more likely to prompt the audience's own confidence in me, even if I feel like I don't entirely know what I'm talking about.

It seems to be a very fine line to tread. I've seen people make very bold statements without having a clue about what they're saying and be regarded as dummies. I've also seen people who do know what they're talking about but cross far over the arrogance line, at which point they once again lost their audience. But I've also seen (too often) very good, sharp, intelligent people be disregarded due to not speaking with enough confidence. It makes me want to beg them not to be nervous, because everyone around them isn't worth being nervous about.

Maybe it's all a part of enjoying your work.