Someone who's hungry has less will power than someone who's well fed.
- a poor man and a rich man are going to work when they each see a dollar coin on a sidewalk. Which of them would bother to pick it up?
- a poor man and a rich man are both drunk after spending a night at the bar. Which one would take a $50 taxi home, and which one will take a bus for $5 (you have to wait 15 minutes for a bus).
- a poor man and a rich man are both hungry and walk by a restaurant for rich people. It would take an extra 15 minutes to walk to a crappy diner for poor people, but a lunch costs 5x cheaper there. Where would each man dine?
Rich man would pick it up, that's $720/hour if it takes 5 seconds. It's things like that that make you rich. Poor guy would probably pick it up too unless he's paranoid people will think he's poor.
>bus
Again looks like huge earnings per hour. He'll take the bus in this example unless he has something very lucrative that he's missing out on, but he's drunk so that's very unlikely.
>restaurant
Depends on the cost of the different places. It might not be worth the time to walk to the other place if the difference isn't great. If he's on a weekday lunchbreak, his time might be better spent elsewhere. Same thing for the poor guy.
And in marshmallow test specifically you don't have kids who are good at business and kids who are bad at business. You have kids of rich parents and kids of poor parents. The fact that the former are supposed to act like pennypinchers, despite not ever having to worry about money or being fed seems counterintuitive to me.
Your whole premise is contradicted by the study.