If prices really can get so unmoored from fundamentals, investors are left with two basic strategies. They can ride the bubble. Or they can bet against overvalued stocks. A naive observer -- i.e., an über free-market economist -- might think that investors will choose the latter path. But, as usual, there's a (possibly apocryphal)** Keynes quote for that -- this time, that
"markets can remain irrational longer than you can remain solvent."
And that's why investors don't always short bubblicious stocks. Not only can a stock stay overvalued longer than an investor can afford to bet against it, but doing so opens them up to potentially unlimited losses for only limited gains.* (After all, a stock can theoretically rise an infinite amount, but it can only fall a finite amount). It's much easier to buy an overpriced asset in the hope that it will keep going up and up -- before unloading it on the greater fool. That's unfortunately a fairly apt description of what the big banks belatedly did as the housing bubble collapsed.
--The Atlantic 2012