The Dow Jones Industrials Average (DJIA) closed below 13,000 today -- the first time since it crossed that mark was on the way up -- on April 24th. Since hitting a record 14,000 on July 19 -- less than a month ago -- the Dow has tumbled 1,139 points, or 8.1%.

I am not sure of many things in life but one thing I can guarantee is that the media will quote "experts" on "what this means for investors." I have nothing to offer here since I have no idea what makes stocks move up and down on any particular day. As best I can tell, the people who control vast swaths of money -- like the $1.7 billion (2006 earnings) man James Simons -- are the ones who know the answer to that question. And the media never gets them to explain.

Nevertheless I have an idea of what is driving the market down -- a credit crunch. There is no money for big leveraged buyouts and the hedge funds are selling their stocks to raise enough cash to pay back the banks to whom they owe as many as $6 for every dollar of assets in their portfolios. I think the market will continue to fall until most of the banks are comfortable that they won't get stiffed on their loans.

Unfortunately I don't know how much stock selling will be required to raise enough cash to satisfy the banks. Nor can I estimate how much the credit crunch will slow consumer spending or crimp corporate earnings. So it would not surprise me if the Dow does not stabilize until it has fallen below 10,000 -- a level it last reached on October 29, 2004.

Peter Cohan is President of Peter S. Cohan & Associates, a management consulting and venture capital firm. He also teaches management at Babson College and edits The Cohan Letter.