Nothing. Standard nature versus nurture confusion. In most every family with multiple kids, there is one that excels and one that should live in the woodshed lest he bring any more disgrace to the family. Both were typically raised the same way with the same rules and attention by the same parents. Why didn't they both respond the same? They didn't because you don't have as much to do with how they turn out as you'd like to think. Or put another way, if you claim responsibility for how the good one turned out, you also have to claim responsibility for the bad one.
At the end of the day, they are going to be who they are with very little input from you. In my case, there were a few small bits that had the greatest impact on who I became and that didn't come from my parents. When I was starting in construction a single sentence from my uncle altered all that I do and would do for the rest of my life.
I was watching a framer sink 16p nails with one hit of his framing hammer and commented that I was impressed. My uncle said the guy was wasting his abilities since that was all he knew how to do. He went on to say that anyone can use their brain to learn how to do anything well and the only limit is your want to.
I applied that. Last week, we cut in some coil over hoops, plumbed in some landscape drain work, finished up some waterproof deck coating, finished building some hand rail on the deck, patched in a section on the flat roof since the roofer can't get here, hung some drywall, taped it off so it could be textured, finished the framing on the mud porch, set the windows, hung the siding, trimmed it out, shot some elevations so the floor leveler can figure a quantity of leveler, and started the painting. It is effortless for me to move back and forth between the things I need to get done because of that one little sentence.