Can’t Grasp Credit Crisis? Join the Club

And it largely explains why the mortgage mess has had such ripple effects. The American home seemed like such a sure bet that a huge portion of the global financial system ended up owning a piece of it. Last summer, many policy makers were hoping that the crisis wouldn’t spread to traditional banks, like Citibank

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[C  Loading...      ()   ], because they had sold off the underlying mortgages to investors. But it turned out that many banks had also sold complex insurance policies on the mortgage debt. That left them on the hook when homeowners who had taken out a wishful-thinking mortgage could no longer get out of it by flipping their house for a profit.

Many of these bets were not huge, but were so highly leveraged that any losses became magnified. If that $100 million investment I described above were to lose just $1 million of its value, the investor who put up only $1 million would lose everything. That’s why a hedge fund associated with the prestigious Carlyle Group collapsed last week.

“If anything goes awry, these dominos fall very fast,” said Charles R. Morris, a former banker who tells the story of the crisis in a new book, “The Trillion Dollar Meltdown.”

This toxic combination — the ubiquity of bad investments and their potential to mushroom — has shocked Wall Street into a state of deep conservatism. The soundness of any investment firm depends largely on other firms having confidence that it has real assets standing behind its bets. So firms are now hoarding cash instead of lending it, until they understand how bad the housing crash will become and how exposed to it they are. Any institution that seems to have a high-risk portfolio, regardless of whether it has enough assets to support the portfolio, faces the double whammy of investors demanding their money back and lenders shutting the door in their face. Goodbye, Bear Stearns.

The conservatism has gone so far that it’s affecting many solid would-be borrowers, which, in turn, is hurting the broader economy and aggravating Wall Streets fears. A recession could cause credit card loans and other forms of debt, some of which were also based on overexuberance, to start going bad as well.

Many economists, on the right and the left, now argue that the only solution is for the federal government to step in and buy some of the unwanted debt, as the Fed began doing last weekend. This is called a bailout, and there is no doubt that giving a handout to Wall Street lenders or foolish home buyers — as opposed to, say, laid-off factory workers — is deeply distasteful. At this point, though, the alternative may be worse.

Bubbles lead to busts. Busts lead to panics. And panics can lead to long, deep economic downturns, which is why the Fed has been taking unprecedented actions to restore confidence.

“You say, my goodness, how could subprime mortgage loans take out the whole global financial system?” Mr. Zandi said. “That’s how.”