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 mattress retailer Mattress Firm Holding (NASDAQ:MFRM) have plunged 16% so far today after its quarterly results and outlook disappointed Wall Street.

So what: The stock has rallied nicely in 2013 on a string of better-than-expected quarters, but today's second-quarter miss -- EPS of $0.41 on revenue of $302.5 million versus Wall Street at $0.51 and $323 million -- coupled with downbeat guidance is forcing Mr. Market to sober up a bit. While the company continues to grow both earnings and revenue at a solid rate -- 40% and 16%, respectively -- the results suggest that it isn't growing fast enough to justify its seemingly lofty valuation.

Now what: Management now sees full-year adjusted EPS of $1.75-$1.83 on revenue of $1.19 billion-$1.21 billion, down from its prior view of $1.90-$1.98 on revenue of $1.24 billion-$1.25 billion. "We expect that the second half of the year will benefit from a return to higher industry-level advertising media spend relative to recent quarters that we anticipate will drive improvement in customer traffic and sales trends in our business," CEO Steve Stagner reassured investors. Given the company's still-hefty debt load and relatively high P/E even with today's pullback, however, I wouldn't be so quick to bet on that bull talk.

Fool contributor Brian Pacampara has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.