When Mr. Bernanke is challenged about the Fed’s performance, he often points out that recognizing a bubble is hard. “It is extraordinarily difficult,” he said during his Senate confirmation hearing last month, “to know in real time if an asset price is appropriate or not.”

Image Ben Bernanke, the Fed chairman, has said it is difficult “to know in real time if an asset price is appropriate or not.” Credit... Tami Chappell/Reuters

Most of the time, that’s true. Do you know if stocks will keep going up? Is gold now in the midst of a bubble? What will happen to your house’s value? Questions like these are usually an invitation to hubris.

But the recent housing bubble was an exception. By any serious measure, houses in much of this country had become overvalued. From the late 1960s to 2000, the ratio of the median national house price to median income hovered from 2.9 to 3.2. By 2005, it had shot up to 4.5. In some places, buyers were spending twice as much on their monthly mortgage payment as they would have spent renting a similar house, without even considering the down payment.

More than a few people  economists, journalists, even some Fed officials  noticed this phenomenon. It wasn’t that hard, if you were willing to look at economic fundamentals. You couldn’t know exactly when or how far prices would fall, but it seemed clear they were out of control. Indeed, making that call was similar to what the Fed does when it sets interest rates: using concrete data to decide whether some part of the economy is too hot (or too cold).

And Fed officials could have had a real impact if they had decided to attack the bubble. Imagine if Mr. Greenspan, then considered an oracle, announced he was cracking down on wishful-thinking mortgages, as he had the authority to do.

So why did Mr. Greenspan and Mr. Bernanke get it wrong?

The answer seems to be more psychological than economic. They got trapped in an echo chamber of conventional wisdom. Real estate agents, home builders, Wall Street executives, many economists and millions of homeowners were all saying that home prices would not drop, and the typically sober-minded officials at the Fed persuaded themselves that it was true. “We’ve never had a decline in house prices on a nationwide basis,” Mr. Bernanke said on CNBC in 2005.