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 consumer bank holding company Green Dot Corporation (NYSE:GDOT) plummeted 18% today after its Q4 results and full-year outlook disappointed Wall Street.

So what: The stock has soared over the past year on better-than-expected growth, but today's Q4 miss -- adjusted EPS fell 42% on an operating revenue increase of just 3.7% -- coupled with downbeat guidance for 2014 is forcing Mr. Market to sober up a bit. In fact, adjusted operating margin fell 590 basis points over the year-ago period, suggesting that Green Dot's competitive position is becoming increasingly expensive to maintain.

Now what: Management now expects full-year 2014 EPS of $1.22-$1.28, well below the consensus of $1.43, on revenue growth of 10%-12%. "[W]e are upbeat about our prospects for growth in 2014 given the previously announced large scale distribution expansion for our Green Dot family of brands, the new product initiatives at Walmart and our growing presence in the Financial Service Center channel," said Chairman and CEO Steve Streit. "Given all of this, we are excited about our company's future opportunities."

More important, with the stock now off more than 20% from its 52-week highs and trading at a forward P/E in the mid-teens, Mr. Market might finally be offering a decent opportunity to buy into those prospects.