Last week, Bill Gross, the so-called bond king, abruptly left Pimco, the investment firm he had managed for decades. People who follow the financial industry were shocked but not exactly surprised; tales of internal troubles at Pimco had been all over the papers. But why should you care?

The answer is that Mr. Gross’s fall is a symptom of a malady that continues to afflict major decision-makers, public and private. Call it depression denial syndrome: the refusal to acknowledge that the rules are different in a persistently depressed economy.

Mr. Gross is, by all accounts, a man with a towering ego and very difficult to work with. That description, however, fits a lot of financial players, and even the most lurid personality conflicts wouldn’t have mattered if Pimco had continued to do well. But it didn’t, largely thanks to a spectacularly bad call Mr. Gross made in 2011, which continues to haunt the firm. And here’s the thing: Lots of other influential people made the same bad call - and are still making it, over and over again.

The story here really starts years earlier, when an immense housing bubble popped. Spending on new houses collapsed, and broader consumer spending also took a hit, as families that had borrowed heavily to buy houses saw the value of those homes plunge. Businesses cut back, too. Why add capacity in the face of weak consumer demand?

The result was an economy in which everyone wanted to save more and invest less. Since everyone can’t do that at the same time, something else had to give - and, in fact, two things gave. First, the economy went into a slump, from which it has not yet fully emerged. Second, the government began running a deficit, as the economic downturn caused a sharp fall in revenue and a surge in some kinds of spending, like food stamps and unemployment benefits.

Now, we normally think of deficits as a bad thing - government borrowing competes with private borrowing, driving up interest rates, hurting investment, and possibly setting the stage for higher inflation. But, since 2008, we have, to use the economics jargon, been stuck in a liquidity trap, which is basically a situation in which the economy is awash in desired saving with no place to go. In this situation, government borrowing doesn’t compete with private demand because the private sector doesn’t want to spend. And because they aren’t competing with the private sector, deficits needn’t cause interest rates to rise.

All this may sound strange and counterintuitive, but it’s what basic macroeconomic analysis tells you. And that’s not 20/20 hindsight either. In 2008-9, a number of economists - yes, myself included . tried to explain the special circumstances of a depressed economy, in which deficits wouldn’t cause soaring rates and the Federal Reserve’s policy of “printing money” (not really what it was doing, but never mind) wouldn’t cause inflation. It wasn’t just theory, either; we had the experience of the 1930s and Japan since the 1990s to draw on. But many, perhaps most, influential people in the alleged real world refused to believe us.

Which brings me back to Mr. Gross.

For a time, Pimco . where Paul McCulley, a managing director at the time, was one of the leading voices explaining the logic of the liquidity trap - seemed admirably calm about deficits, and did very well as a result. In late 2009, many Wall Street analysts warned of a looming surge in U.S. borrowing costs; Morgan Stanley predicted that the interest rate on 10-year bonds would soar to 5.5 percent in 2010. But Pimco bet, correctly, that rates would stay low.

Then something changed. Mr. McCulley left Pimco at the end of 2010 (he recently returned as chief economist), and Mr. Gross joined the deficit hysterics, declaring that low interest rates were “robbing” investors and selling off all his holdings of U.S. debt. In particular, he predicted a spike in interest rates when the Fed ended a program of debt purchases in June 2011. He was completely wrong, and neither he nor Pimco ever recovered.

So is this an edifying tale in which bad ideas were proved wrong by experience, people’s eyes were opened, and truth prevailed? Sorry, no. In fact, it’s very hard to find any examples of people who have changed their minds. People who were predicting soaring inflation and interest rates five years ago are still predicting soaring inflation and interest rates today, vigorously rejecting any suggestion that they should reconsider their views in light of experience.

And that’s what makes the Bill Gross story interesting. He’s pretty much the only major deficit hysteric to pay a price for getting it wrong (even though he remains, of course, immensely rich). Pimco has taken a hit, but everywhere else the reign of error continues undisturbed.