In my case my parents were either too busy raising five kids all born two years apart, in the case of my mother, or a father who was away for six years of my life fighting as a soldier in WW2. When the war finished I rarely saw him except for very short periods on weekends. So I cannot blame Nurture, good or bad, on my self-confidence or otherwise.
I was quite shy as a child. However,I think what gradually brought on today's confidence - and it is there, I've spoken to a thousand audiences ranging in number from half-a-dozen to a couple of hundred people - to my years in the Navy. I served on small ships, two on which I was the only radioman aboard.
Even so, I found that my gaining in 'self-esteem' came from a lifetime of sustained study, different types of work, and always aiming to becoming a better me in all three areas of life: body, mind, and spirit. I believe in lifetime learning and I'm still at it at seventy-nine.