I don't believe I said it is unattainable, only that the deck is stacked against them. As we speak, the 20 million millionaires are just 6% of the population of the states. Being a millionaire alone doesn't really make you "upper class".
I know that regardless of how much I make, in my heart I will always be a prole, and that will never change because I lack the mannerisms and the connections said people. I grew up in a different world, and even if I were to spend every waking hour with them, things wouldn't change, and frankly I am not interested in it either.
The way it works (and has always worked if the historical novels are at all accurate) is that you make the money, and then put your kids in the "good schools" and donate a building or two, and their kids (your grandkids) will then be upper class. Part of this is often having enough money so your kids can marry into "upper class but destitute" families, of which there is always a steady supply.
It's worth observing that according to traditional Irish law, there was an explicit process for ascending to lordly status, and it required three generations to complete. So the three-generation model sees some replication cross-culturally.
If you didn't want to wait that long, traditional Irish law also allowed you to purchase an equivalent-to-lordly status for yourself. You held equal rank with actual lords, but there were two major downsides: (1) this was a tremendous ongoing expense, more than many actual lords could have afforded; and (2) unlike true lordship, your status was not hereditary.
I know that regardless of how much I make, in my heart I will always be a prole, and that will never change because I lack the mannerisms and the connections said people. I grew up in a different world, and even if I were to spend every waking hour with them, things wouldn't change, and frankly I am not interested in it either.