"The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money. Take boots, for example. ... A man who could afford fifty dollars had a pair of boots that'd still be keeping his feet dry in ten years' time, while a poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet." - Terry Pratchett
The fact that being poor is expensive is, in fact, the root cause of why it is so difficult to escape poverty.