What best predicts how a life turns out?

Everyone names a different lever: IQ, grit, self-control, the family you're born into, the warmth of your closest relationships. Longitudinal studies each crown a different champion: Dunedin on childhood self-control, the Harvard Grant study on relationships, others on raw cognitive ability. Is there one strongest predictor of how a life turns out, or does 'success' split into separate outcomes that each answer to a different cause?

open-question·psychology·success