I remember reading an interview (probably in one of Jack Schwager's Market Wizards books) with a guy who had been a Wall Street analyst. He kept the news reports of the day sorted into "good news" and "bad news" piles on his desk. When a journalist called to ask why something had gone up that day, he'd cite whatever was on top of the good news pile. When asked why something had gone down, he'd cite whatever was on top of the bad news pile.
In short, markets move around for a whole host of random reasons.
The nightly news 'the market moved lower on profit taking' or 'the market moved higher on positive news X' is just rubbish.
Occasionally, there is a cause-and-effect like an unexpected interest rate change, or a better-than-expected sales figure in a key industry, but for the rest of the time, it's just random movement.
The worst thing is the need to commentate on it confuses the correlation in the general publics mind, so people believe you can talk the economy up or down, which is an assertion I don't agree with.
