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 office supply retailer Staples (NASDAQ:SPLS) sank 13% today after its quarterly results and outlook missed Wall Street expectations.

So what: The stock has soared over the past year on continued market share gains in the U.S., but today's second-quarter results -- income fell 15% on a revenue slip of 2% -- coupled with downbeat full-year guidance reignites concerns over its struggles abroad. In fact, international sales in the quarter fell 8.3% over the year-ago period, suggesting that its business model is a bit more sensitive to global weakness than analysts had thought.

Now what: Management now sees full-year operating EPS of $1.21 to $1.25 and a revenue decline in the low single digits, well below its prior view of $1.30 to $1.35 in earnings and a revenue increase in the low single digits. "We continue to make progress on our strategic plan to reinvent Staples," Chairman and CEO Ron Sargent said in a statement. "We drove online sales growth and aggressively managed expenses during the second quarter, but this progress was offset by weakness in our retail stores and international businesses." Of course, with the stock now off about 16% from its 52-week highs and trading at a still-cheapish forward P/E around 10, those headwinds might finally be discounted into the price.