Just when the market felt like they'd found a trading pattern that was reliable - buy on Tuesday - the market couldn't get out if its own way today. The market had been up on ever Tuesday this year. This is just a crazy coincidence, but in the current computer driven markets it has been a reliable trading indicator.
Unfortunately, today was the exception that proved the rule. That momentum names in the tech sector were very heavily influenced by the fall of Twitter which hit a new all-time low today. Today was the first day that the stock could be sold by insiders and despite assurances that they would not be selling, nearly 20% of all of the stock in the company traded today which meant someone was lying and plenty of people were selling.
Well, maybe the computers will decide they like buying on Wednesday :)