In February of last year, The Wall Street Journal reported that the top 10% of households by income —those earning around $250,000 or more— now account for 49.7% of total spending. It's a staggering percentage, one that can tilt an entire economy toward the top.

If we expand the analysis to the top 40% of earners, that percentage rises to more than 75% of total spending. This means that the poorest 60% of Americans represent less than a quarter of total spending. In short, rational economic decisions at the individual level are driving the entire economy to favor the richest. And if the richest 10% are by far the primary consumers, even members of the upper middle class will struggle to feel secure.

If you're a car manufacturer, do you want to build low-end cars with thin profit margins? Or do you get higher profits selling SUVs with fat profit margins? If you're a real estate developer, luxury housing is often much more profitable.

Yes, used cars can still be very good, and there's evidence that building more luxury housing can lower prices by increasing the overall supply, but the American middle class is the one getting used cars. The shiny new stuff? That's for others.

The result can be a constant feeling of being a second-class citizen. You check into hotels looking for the shortest line for Gold members. You pass by the Preferred members' kiosk on the rental shuttle bus, where frequent travelers simply grab their keys and go.

Or, much more importantly, you move to a new city and discover that the wait to see a new doctor can stretch for months, unless you can afford the hefty monthly fee for concierge medicine. In that case, you'll be seen immediately, perhaps with the added benefit of getting Botox if you're middle-aged.

And if you live in a city that the top 10% love? Well, even being upper middle class doesn't feel rich at all. Six-figure salaries buy tiny apartments, and everything from food to gas costs a fortune. Soon you find yourself Googling real estate prices in Chattanooga or Des Moines —surely it's cheaper there— whether or not you intend to move.

In this context, "affordability" refers not only to the cost of a specific good (nor even necessarily to the rate of inflation at a given moment), but rather to the entry price to what should feel like a normal American life, one that includes baseball games with the kids, a doctor on call, a house you like, and at least the basic sense that you haven't been left behind.