So much research, so much money and so many theories.
Humanity as whole has (is) always been intrigued about what differentiates people who succeed from those who fail.
Just google why do people fail succeed and browse the over-6-million results to see how fascinated we are by this topic.
So let me summarize it all for you, in one simple sentence:
The only 100%-sure difference between people-who-succeed and people-who-fail is that those who succeed continued trying(*).
Read it again. And try again. And again. If you haven't succeeded yet, the single-most-meaningful thing you can do in order to succeed - is to keep on trying.
Analyze you failures. Improve on your efforts.
But most importantly - keep on trying!
As Thomas Alva Edison is rumored to have said after finally getting the lightbulb to work - after 10,000 failures:
I have not failed. I've just found 10,000 ways that won't work.
(*) Well, with the exception of people who who "got it right the first time". Rumors are such people do exist.