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 The ExOne Company (XONE) sank as low as 10% today after the 3-D printing company cut its revenue guidance for 2013.

So what: The stock has rallied over the past month on optimism over accelerating growth, but management's downbeat guidance -- 2013 revenue now expected at $40-$42 million versus a prior view of $48 million -- is forcing Mr. Market to quickly sober up. While ExOne blamed the shortfall strictly on revenue-timing issues, analysts are interpreting it as a sign of poor visibility going forward.

Now what: Management remains confident that it will be able to hit its 40%-50% annual organic revenue growth target again in 2014. "We continue to see the industrial market evolving toward 3D printing and are pursuing opportunities to expand our strategies," said Chairman and CEO S. Kent Rockwell. "We have made a substantial effort for a company our size to undertake the acquisition strategy that we announced in our follow-on offering completed in September 2013, and we have incurred expenses in the fourth quarter of 2013 related to such efforts." More important, with the stock now off about 30% from its 52-week highs, it might be an opportune time to buy into that bullishness.