"Robust markets like major stock indices are fairly good at incorporating information. They don't literally have to see an event occur in order to "price in" its effects. On Wednesday, for example, Barack Obama signed the stimulus package into law. Once this occurred, the prospects for the passage of the stimulus rose to 100%. But what had been the probability of the stimulus bill passing the very second before Obama put pen to paper? Probably about 99.999999%, accounting for the small probability of a hostile takeover by space aliens in the intervening moments. The performance of the market in reaction to such events tells us no more about how it feels about them than it does to the rising of the sun."