People's outlook for the economy changes much faster than the underlying state of the economy. The Fed tries to keep its eye on the larger ball and not on the ping-pong ball of the stock market.
Probably the easiest way to think about the Sept. 11 event is to think of bouncing a ball off the roof of a garage onto the driveway, ... The ball's bouncing around, and it's still unclear what the slope of the driveway is. But we can be fairly sure it's sloping up.