This might be culturally dependent, as in some cultures there is much more emphesize on competition than in others. Have you reflected on your behaviour towards your children with respect to this?
I think there is a significant (inherent or deeply ingrained) personality component to people’s initial outlook. E.g. there was a pair of fraternal twins who we used to play with at the playground, and one of the pair was much more willing to try things while the other was much more afraid of being judged. More generally I have regularly seen substantial differences between siblings despite a lack of obvious differential treatment from their parents or any change of cultural values/norms.
Kids of 2–4 years old seem to have similar range of behaviors across substantially different cultural groups, e.g. comparing kids raised by tolerant non-confrontational hippies vs. strict immigrant professionals.
I imagine that learning to be comfortable as a beginner is something that can be trained / practiced. Some people certainly improve at it as they get older.
