There has to be so many things at play. It’s definitely not one thing.
Opportunities - making opportunities available to the child, whether it’s hobbies, tutoring, clubs, sports etc.
Ability - if they already have an academic ability it’s going to be so much easier. If they don’t do they have drive and ambition to work hard?
Networking - if they want to break into a certain industry it’s going to be so much easier if there are contacts there
Good mental health - this sits alongside confidence. It doesn’t matter how bright you are, if you suffer with anxiety or similar it’s going to wreck havoc on future job prospects
Parent availability- I think ALL children do better when parents are available to them. Even if you only have a small amount of time, put your phone down y actively listen.
Stable home life - the more adverse childhood events a child has the more likely they are to have problems in adulthood. By problems that could be anything from poor mental health to addiction and criminality. Children with calm, stable home lives are so much more likely to fair better in every area.