In Terry Pratchett's excellent Discworld series of satirical fantasy books there is a character names Sam Vimes, who is the head of the Night Watch, and later commander of the City Watch. While he eventually progresses over the course of several books to a fairly prosperous position, he started out in the poorest part of the city, and developed this theory.
Basically, he says, as a watchman, his pay is about $38 a month. He's on his feet constantly, and his boots are an essential tool of his trade (literally "shoe leather" police work). A really good pair of boots, that would hold up for years, cost about $50, but all he can afford on his pay are cheap, $10 boots. He may wear out several pair of these a year, even if he cuts cardboard to patch the worn out soles when he can. Over the course of 5 years, the man in the good boots has only spent $50, while Sam has gone through 10 or 11 pair of boots, costing him twice as much and - here's the kicker - he still has wet feet!
This theory applies in our modern world not only to consumer goods, but to utilities, food and even finance as well., any area where those who can't overcome the initial investment barrier on something durable are faced with paying over and over for an inferior product. For example, banks charge fees on many types of accounts if they have less than a minimum balance, and the worse your credit is, the higher your interest rates on any sort of loan or credit card (yes, it's possible for people who have plenty of money to ruin their credit, but that's a different matter, I'm talking about the 15-20% of Americans to whom "living beyond your means" means "eating regularly, having transportation to work and sleeping indoors").
Add to this the requirements for getting a job, many of which require, at the very least, a good suit ($500-800) for an interview and a reliable car (several thousand dollars for anything that can be considered "reliable, paid in cash up front unless you can get a loan, which carries its own penalties, plus fuel, maintenance and insurance) and, if the job pays any kind of living wage, likely at least a bachelor's degree ($$$$$$$$$$).
Now, before you think I'm clamoring for some sort of Great Communist Revolution (those usually end pretty badly), relax a bit. It very much IS possible to get out of the poverty trap, but it requires a lot of work, more than a little luck, and a lot of good decisions. Unfortunately, we're not necessarily educating people on how to make those decisions, so they end up spinning their wheels and wasting their potential.
Mostly, at the moment, I'm just sharing an interesting way of looking at the problem, and something I've seen personally (been on "that job-car-education" wheels a time or two) in action. Also, I'm recommending that if you haven't read the Discworld books, you give them a go, they're good, funny reads that will get you thinking, which is about the best recommendations I could give any book.