Debt is a vicious cycle, and perhaps the most likely financial factor to inhibit the growth of wealth over the course of generations, (ensuring that the poor stay poor and the rich stay rich). It's great that your parents were able to increase their wealth by being frugal, but the opportunity to do so often tied to some form of privilege, whether earned or unearned - their case study stands in contrast to the millions of working poor, and extremely impoverished people inhabiting the globe - who are unable to increase their net worth or buying power despite working very hard, and spending frugally as a default because they have precious little alternative. Still, this article is great advice. :)
Yeah the way they were able to do it is by living frugally through college in a trailer. They then were teachers for several years living in the same trailer they pulled to the school district they worked in. Then they were able to get comparatively high paying jobs working for a General Motors. So they had decent pay in comparison to how frugal they were. They still live extremely frugally and everything is paid off. In my mind they have never really got out and enjoyed their savings. They are very simple and don't really like to travel for some reason.