> But in a poor household, taking the marshmallow now is likely the optimal choice since there might not be any later — even if your parents tell you to wait. That’s not necessarily a sign of anything but having adapted to a particular environment: times you listened led to a negative outcome, so you stopped.

You've repeated the whole thesis from the article: people are conditioned for delayed gratification if that is possible/predictable, and then asserts that parents have the influence to develop that trait in kids by fostering predictability.