How often have you heard the bromide about how the rich get richer and the poor get poorer?

Well, it’s difficult to look over this year’s list of the wealthiest Angelenos, which is in the May 18 issue of the Los Angeles Business Journal, and declare that that’s true. By our count, 41 of the 50 wealthiest Angelenos lost money over the last year, and eight of them lost more than $1 billion each. Only three on the Business Journal’s wealthiest list actually gained money. On the whole, the rich certainly did not get richer.

Now, I know some could argue that this is only one year and an aberrant one at that, so it doesn’t really count. Over time, the rich do get richer and the poor, poorer.

What’s more, those who so ardently believe that also seem to believe that wealth is almost a semi-permanent state. It’s the result of what’s basically a rigged system in which the privileged few who inherited good fortune can accumulate wealth with no serious danger of falling into the dark depths of middle classdom. The poor are unfairly trapped and can only dream of escaping, maybe via the lottery or a TV game show.

That’s an interesting argument. Except for one teensy little problem: The facts just don’t prove it. Americans have gradually been getting wealthier.

According to U.S. Census data released last year, the share of households earning a middle-class income of between $35,000 and $100,000 did shrink from a decade earlier, but so did the share of those earning less than $35,000. Only the share of households earning more than $100,000 grew, as it has in the past. (And yes, the income amounts were adjusted for inflation.)

In other words, it’s not just the rich who are getting richer, pretty much everyone’s getting richer.

Those who believe that the rich and poor are stuck in their classes apparently are blind to the tremendous dynamic movement between income groups; people regularly move up and down the wealth and income scales. Folks classified as poor may be young adults starting out. Many of them soon migrate into the middle class and some vault into the upper class. They retire and again may be classified as poor, based on income, even if they are sitting nicely on their next egg.

If you still don’t believe there’s dynamic movement, just look at some of the profiles in the Business Journal. Some inherited wealth, to be sure, but plenty did not. Jeffrey Greene, for example, was a working-class kid in Massachusetts who started doing odd jobs at 10 and had to work his way through school, but made $800 million on a savvy bet against subprime mortgages and now is a billionaire who owns one of the biggest mansions in Los Angeles.

Likewise, there’s plenty of movement down. Kirk Kerkorian lost an estimated $5.3 billion over the last year on bad bets on Las Vegas and the Ford Motor Co. Another year or two like that, and Kerkorian won’t be wealthy any more. That’s the kind of upset that can happen when one plays the game of capitalism.

Clearly, losing wealth is not good. We all hope that steep drops like we’ve seen lately will be rare in the future. Still, this kind of tumult is a reminder that our system is dynamic and responsive. Breathtaking wealth can be accumulated and can be lost, sometimes spectacularly so.

The point is Americans are not stuck in socioeconomic classes. It is perfectly possible for a working-class kid to become a billionaire. And it is quite possible, as the Business Journal demonstrates, for them to lose it.