Poverty is also thought to have caused the diffidence in performance in the marshmallow test[1]. Poor kids learn to take advantage of the moment and distrust the future. And poor kids tend to be lower earners in later life than wealthier kids due to advantage differences[2][3]

[1]https://en.wikipedia.org/wiki/Stanford_marshmallow_experimen...

[2]https://www.theatlantic.com/family/archive/2018/06/marshmall...

[3]https://journals.sagepub.com/doi/abs/10.1177/095679761876166...