Fortune has an interesting story on the worst housing markets for 2009. 2008 was a brutal year across the country, but the experts predict that it will get a lot worse for quite a few cities over the next 12 months. Los Angeles is expected to see a decline in the median home value of 24.9%. Miami Beach is expected to plunge 22.8%. Washington D.C. rounds out the top 10 worst markets with an expected decline of 19.9%.

But if those predictions are to be believed, you would have to be a complete idiot to buying real estate in any of those cities now: And therein lies the problem with predictions: If everyone knows they're going to go down that much next year, that's unlikely to happen because the decline will happen this year instead. If everyone thinks a stock is going to go from $5 to $10 over the next year, it will go to $10 now: And then, who knows what will happen? That's the problem with conventional wisdom. In financial markets, its predictions must be wrong.

It's worth remembering how few experts predicted the huge price declines of the past year: If they had, the declines would have happened the year before! So many of these predictions are really just extrapolations of past events.

What will happen to real estate over the next year? I'm smart enough to know that I'm too stupid to know. But I think people should be skeptical of anyone making big predictions for big price declines.