I never really understood how to speak confidently in any gathering. (Yeah, yeah, the litany of what I never understood is long. So? You, of course, understand everything from the Big Bang to the String theory, from Nanotech to drones...good for you.) More often than not, I start bleating, "But..." and get drowned out by others who hardly seem to have noticed that I even opened my mouth. (Halitosis may have been a help, perhaps, in getting people to notice when you open your mouth. What is Halitosis? Well, you know everything, don't you? Why ask me?)
And then some chap pops up saying, "Well, simple! All it takes is to become an expert in the subject you want to speak about. Then it is easy to be confident." Umm! That is too much work. And, you know, it is not quite as easy as it sounds. I mean, I speak to other finance people about a project appraisal and...well, what if I am wrong? Or have forgotten something? Or...you see, it is all fine to talk of being an expert and, thus, confident but the issue is that I need to first be confident that I AM an expert. Now that...
But, then, when it comes to talking about the same project with other friends...now there I am confident. Interesting, come to think of it. I actually get even more confident talking about what's wrong with the management of the country's economy, especially when a lot of the people around me share similar views. (As in, come on, if you think high income taxes are counter-productive, are you really going to find much opposition in any given group of people, except if they all happen to be members of the ruling party?)
Perhaps I am on to something here. I mean this 'Know your subject' is all very well for confidence, though it is sort of tougher on you, since expertise is not something that you can instantly order on Amazon even if you have an Amazon Prime membership. But it is not really necessary, you know.
What is important is not that YOU know your subject; what is important is that others do NOT know that subject any more than you do or, ideally, far less. It is not YOUR knowledge that will give you confidence but your audience's ignorance. When you choose to speak to an audience, speak not of what they are likely to know but of what they are likely to not know.
So, the mantra for confidence is 'Know your audience'.