Young vs Old - The secret of self confidence

Self confidence is something I had decided was based on personality. Some people were just naturally more self confident.
I was thinking about this because my daughter had just auditioned for a musical. I expected her to walk of the audition nervous and worried, as I would have done. I could not have been more wrong. She walked out proclaiming her excellence.
When I once complemented her on a singing performance. She replied offhandedly, "Of course. I told you I could sing."
I wondered where she got this endless supply of self assuredness? It wasn't from my genes.
Then I remembered as a kid I had also auditioned to get a part in a school musical. I was also chosen. This was despite only a few weeks earlier auditioning and failing to get into the school choir. I cannot remember what made me think it would be a good idea to audition for a solo singing part after failing to get into a choir. Perhaps as a kid, it never occurred to me not to try.
If I Google self confidence I received 116 million results mostly on how to improve it. If I look up self  doubt there are 110 million results mostly on how to diminish it.
It is something many people wish to change about themselves.
So how has my daughter succeeded in developing it in only eight years of life?
My lectures about how the world works and that success is not always guaranteed, before she throws herself into something, continue to go unproven for her.
The quote in wikipedia on self confidence attributed to Professor Raj Persaud says that true self-confidence comes from an attitude where you: "Promise yourself, no matter how difficult the problem life throws at you, that you will try as hard as you can to help yourself. You acknowledge that sometimes your efforts to help yourself may not result in success, as often being properly rewarded is not in your control."
I don't think most people who look up the 116 million results for self confidence are looking for true self confidence, they just want to feel better about their abilities. I am not sure my daughter has true self confidence by that definition.
She knows how to celebrate her own success without comparing it with others. Three other children also were accepted at the same time as she auditioned. She was happy for them too but she didn't think their success made her any less skilled.
If life throws her something hard, she also doesn't necessarily try to fix it. She is a kid, for her that is what parents are for - to deal with the hard stuff. Usually her approach is I am not good at that - but look how good I am at this!
I think limited life experience also helps.