Breifly, what banks do

To grasp the problem, you need to understand what banks do.

Banks exist because they help reconcile the conflicting desires of savers and borrowers. Savers want freedom — access to their money on short notice. Borrowers want commitment: they don’t want to risk facing sudden demands for repayment.

Normally, banks satisfy both desires: depositors have access to their funds whenever they want, yet most of the money placed in a bank’s care is used to make long-term loans. The reason this works is that withdrawals are usually more or less matched by new deposits, so that a bank only needs a modest cash reserve to make good on its promises.

But sometimes — often based on nothing more than a rumor — banks face runs, in which many people try to withdraw their money at the same time. And a bank that faces a run by depositors, lacking the cash to meet their demands, may go bust even if the rumor was false.

Worse yet, bank runs can be contagious. If depositors at one bank lose their money, depositors at other banks are likely to get nervous, too, setting off a chain reaction. And there can be wider economic effects: as the surviving banks try to raise cash by calling in loans, there can be a vicious circle in which bank runs cause a credit crunch, which leads to more business failures, which leads to more financial troubles at banks, and so on.

That, in brief, is what happened in 1930-1931, making the Great Depression the disaster it was. So Congress tried to make sure it would never happen again by creating a system of regulations and guarantees that provided a safety net for the financial system.

And we all lived happily for a while — but not for ever after.

Paul Krugman, "Partying Like It's 1929", The New York Times, 2008년 3월 21일.

He's extremely brilliant.