Upward mobility still occurs in the US, at all levels. While the advice is difficult, almost impossible, for most to apply, it is sometimes applicable.

One of the main issues is that a lot of advice is presented as an unconditional, absolute guarantee to success. A college degree was never a guarantee of future success (contrary to great-grandparent's assertion), but the push to get everyone to get a college degree has rendered its utility as a helpful marker much more useless. Similarly, the ability to start your own business is difficult for most people, but even for poorer individuals, it is possible to start, say, a cleaning service with very little assets. (At the same time, such businesses are unlikely to make a whole lot of money at the end, but you might be able to move from working class to middle class, e.g.). A lot of contractor businesses--your plumbers and the like--are going to be from the lower middle class or middle class, and you can make some good money there, although that is also likely to be at the cost of your health much sooner than you expect.