Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Zynga Inc (NASDAQ:ZNGA) were down more than 16% as of 1 p.m. Friday after the company announced weaker-than-expected fourth-quarter results.

So what: Quarterly revenue climbed 9.2% year over year to $192.5 million, which resulted in an adjusted net loss of roughly $2.5 million, or closer to $0.00 per share. Bookings -- which are Zynga's key measure for in-game virtual goods purchases -- grew 24% year over year to $182.4 million, including a 120% increase in mobile bookings over the  year-ago period. Unfortunately, analysts were looking for a roughly break-even quarter on higher sales of $201.1 million.

In addition, Zynga expects current-quarter revenue in the range of $155 million-$165 million, while bookings are projected to be $140 million-$150 million. That should result in an adjusted net loss per share in the range of $0.03-$0.02. Wall Street, for its part, was modeling another break-even quarter on significantly higher revenue of $200.9 million.

Zynga also announced the closure of its Zynga China studio, which will affect 71 employees and result in annualized cost savings of around $7 million.

Now what: Mobile bookings represented 60% of Zynga's total in Q4, thanks to an 87% increase in monthly mobile consumers over the year-ago period. It makes sense, then, that Zynga is hitting mobile hard, with CEO Don Mattrick stating, "We will deliver a 100 percent mobile-first new product slate featuring new games, with a goal of ending 2015 with more than 75% of our fourth quarter bookings coming from mobile."

Even so, that's little consolation for investors if the company can't achieve sustained profitability in the process. And while a couple of big hits could certainly right Zynga's ship, I'm personally still skeptical of the difficult economics behind the free-to-play game industry. As a result, it's hard to blame the market for bidding down Zynga stock Friday.