What I've read so far, combined with my personal experience, tells me that we are born with some important biological distinctions, but that their influence often pales in comparison to the dramatic variety of stimuli we experience from the first moment of our lives. I'm particularly fascinated by the 1995 Hart/Risley study on parental language and encouragement (more on their book here), and by the study's interpretations (solidly pro-environment here and here; somewhat equivocal here).
Effort and desire are obviously paramount, and while I'm open to gene-driven personality factors that would make someone intensely motivated, it's always seemed to me that desire has a big psychological component.
Before I gave it up for the guitar years ago, people used to call me
a "talented" violin player, which made me laugh because it had taken me
so long to make a non-ear-splitting sound. I went from
deranged-sounding to award-winning, but that took years and gobs of
practice. Same thing with writing. I don't compare my abilities to
Albert Einstein's, but his quote about success does resonate strongly
with my experience: "It's not that I'm so smart. It's just that I stay
with problems longer."
I also know the opposite feeling. Being mediocre to poor at most things, I know that, in a million years, I could never be a stupendous soccer player or painter or mathematician. But my experience with how long and hard it has taken to get good at other stuff tells me that these things look impossible mostly because they're so far away.
Here is the strangest and most enticing thing about this subject: the invisibility factor. We see people being good at stuff -- we don't see them becoming good. I want to try to make the process visible.