Poorer people tend to value temporary "happiness" over long-term happiness. This means that someone would rather buy a car or take a vacation by going into debt, rather than holding off on that purchase and being able to have the things that matter in the long term, like money to spend time with family, or money to support every day activities that increase one's quality of living.
The other example of poor money management involves the lottery. Some people tend to over-estimate the probability of winning because they think that if they keep playing, they are more likely to win. Part of this has to do with the gambler's fallacy where each time they lose, they think they have a higher chance of winning. Some people also rationalize thinking "someone has to win", which is a poorly thought out way of saying the chances are better than they really are.