"Never give a sucker an even break. Never wise up a chump"--W.C. Fields

People will scratch their heads for weeks trying to figure out why the Dow turned around about 600 points today and ended up 300. It is the kind of day folks can can tell their grandchildren about.

Part of the big jump in the Dow was due to the big run in financial components of the index, especially Citigroup Inc. (NYSE: C), American Express Company (NYSE: AXP), and JP Morgan Chase & Co. (NYSE: JPM).

The rise was based on "what the Fed did yesterday and prospects for next week," said Peter Boockvar, equity strategist at Miller Tabak in an interview with MarketWatch. That is really no explanation at all. The market is not blind to what the Fed did or what it is likely to do. But no one had a better explanation.

Less than three months ago, the Dow was over 14,000. Today it dropped as low as 11,645. Traders saw some bargains in depressed shares and rushed to get a piece of them. There is no guarantee that many of those people will not take profits a day from now or a week from now. There has been no fundamental change in the dynamics of the market or the economy. No one will know if the Fed move has worked until a few months from now. The stimulus package that the President and Congress are working on could still fall apart.

Any rally now is based in part on a belief that the economy will not fall apart like a cheap watch. That way of thinking would be a mistake. If the next two months are riddled with higher-than-expected home foreclosures or some despot manages to interrupt the oil supply from a big exporter of crude, the market could sell off 5% or 10% again.

The tooth fairy may still exist, but her pockets are empty.

Douglas A. McIntyre is an editor at 247wallst.com.