I think, nature defines who you can become and nurture can mess with it or better it, but if there is no potential in first place, nurture can't do anything about it. When you bake cookies, the dough is the important factor. Of course when the oven is maladjusted, it can ruin the cookies or make the cookies better, but if the dough is just shit too begin with, then the oven can have the best temperature conceivable, it still can't repair the damage the bad dough has done.
but things like confidence is all down to nurture
Yes, but where does that come from? If you're ugly (nature), stupid (nature), very short/weak (nature), mentally or physically ill (really depends, but a lot of them are nature, some are admittedly nurture) or anything else, then you will be treated badly by other people, which will lead you to have low confidence. It's all a doom loop of misery.
