How would you model something like 9/11?  There are too many random events that occur every trading day.  Some are good.  Some are bad.  The best we can really hope for is that we notice things are going to hell before everyone else does.  That allows us to get out early and save our own ass.  That's the truth about the markets.  The models we have help us to understand things during relatively normal times, but they are just models.  You can't rely on them 100% of the time.  At some point, you have to ask yourself, "Does this make sense here?"