Depending on who you ask:
Group 1: "Well, it's a random walk based on noise around individual actors and their particular trading strategies, which are altered slowly or quickly based on macro and stock-specific factors, and in this case, the net balance is a slow decline, but there's not enough public data to be more specific than that."
Group 2: "Well, if you take a look at the Bollinger Bands and take into account Fibbonacci Retracement...."
Group 3: "Damn short selling bear raiders aided by naked short selling from MMs!!!!"
(I'm in Group 1, BTW
)