There's a lot of selling pressure over the last few trading sessions on the SPYs and the QQQQs. I've drawn a line from the long down bar days to the corresponding volume to clearly illustrate the situation. Also notice both markets are right at their upward trend lines.
Today the markets were caught between the bulls and the bears. The bulls looked at the inflation report and thought the Fed could lower rates. The bears looked at Home Depot and Wal-Mart earnings and saw a slowing consumer.
The markets could go either way right now. While there's a ton of liquidity in the system right now (see this post), there is also a psychological need for a correction.