Based on a book I just read called Poor Economics by Abhijit Vinayak Banerjee and Esther Duflo, it is true that extremely poor people are much, much less able to make and follow long-term plans than rich people. They suggest it has to do with various facets of a very poor person's life (for example, the difficulty of getting loans or even opening a savings account) and also with the "willpower depletion" aspect, because the everyday lives of the poor include so many small decisions that are made automatically by the societies that rich people live. Also, their research established that poor people, even those poor enough that they can't afford enough food to eat, still spend money on short-term luxuries, like sugary tea.

Good book to read. I would recommend it.

Seconding that and upvoting since I can't see why this should be negative.