I think it can be many things. Buying habits like a large utility bill or a car. A wealthy person (or someone with savings) can pay it outright without any issue whereas the poor need to pay in installments with interest.

Debt and interest repayments continue to roll over without any increased income traps them in a vicious cycle.

Still a savings mentality seems to get people out of poverty. You can see this with migrants in wealthy countries. They start with nothing and over a generation set themselves and their kids up for a prosperous future.