What most people don't understand is that confidence is a byproduct of mastery. Bravery, balls, guts, and adrenaline, in my opinion, is confidence without mastery. It's not bad to have confidence without mastery, but it seems like that is culturally valued over having confidence with mastery.
A lot of people struggle with not having confidence or feeling like they're chronically nervous (this used to be me). But what I've realized is that it is completely natural to be nervous if you are doing something you have not mastered.
I overcame public speaking because I got good at it, not because some crazy adrenaline took over. It was a journey, but I got good at it before I got confident in doing it. I used to be scared as heck to speak in front of people because I didn't know what to say, I didn't know how to perform well in front of people, I was nervous about what other people thought, etc etc.
But when I started getting good at it, I realized that speaking about something you don't understand very well is very daunting, and that confidence is natural if you are speaking about something that is a part of who you are, something you deeply understand, and want to share.
How hard is it to publicly speak about something you're a master in? Sure, you might not be articulate and concise, but that's another issue that can be overcome.
Here's a general outline:
Noob --> Amateur --> Getting the hang of it --> Competence --> Proficient --> Excellent --> Master
Noob: mostly nervous, feel completely over your head
Amateur: a few aspects are getting familiar, still mostly nervous, little confidence
Getting the hang of it: mild confidence, still feels daunting at times, you begin to recognize the basic factors of doing well
Competence: Solid grasp of the basics, perform well more often than not, mild hang-ups
Proficient: good consistent performance, you get "in the zone" often, learning the little idiosyncrasies of your craft
Excellent: everything is completely natural; cruise control
Master: Cruise control AND innovating and pioneering because you understand all the ins and outs of the craft
I totally just made all that up based on my experience. This can range anywhere from breaking habits, learning piano, learning guitar, learning a new computer game, learning a language, learning a new trade, learning a new career, etc etc.
So for me, because I understand that confidence is a byproduct of mastery, I'm pretty confident even when I start out something new. I'm not confident in my current performance, I'm just confident that I'm going to get really good at it if I keep doing it.
So I never get into something new thinking, "man this is gonna suck cause I have no clue what i'm doing," I always go in thinking, "I'm going to learn this, and I'm going to get good at it."
Failure is now the quickest way to learn and move towards being a master instead of an embarrassing result of being new at some daunting task.