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 Rule Breaker pick Green Mountain Coffee Roasters (Nasdaq: GMCR) are switching to decaf this morning, getting hammered by as much as 14% today with little reprieve as renowned hedge fund manager David Einhorn made negative comments about the company at the Value Investing Congress in New York.

So what: Einhorn, president of Greenlight Capital, has shorted the K-cup maker for a variety of reasons, including a "litany of accounting questions," outpaced capital expenditures, and "looming patent issues." In addition, Whitney Tilson, who made headlines with his public bearish debate with Netflix (Nasdaq: NFLX) CEO Reed Hastings earlier in the year, has come out and disclosed he is also short Green Mountain shares.

Now what: Green Mountain has been on a streak for the past couple years, and if you bought in when this stock was first recommended by our Rule Breakers team, you'd be sitting on an 818% winner. Einhorn believes that the company's earnings are "too good to be true." Whenever you have a stock that has a run like this and skeptics pop up, it's always good to check your initial investment thesis and see if it still holds. Einhorn is known for capitalizing on the financial crisis -- he was short a handful of financials, including Lehman Brothers -- so his statements are bound to draw a lot of attention.

Interested in more info on Green Mountain Coffee Roasters? Add it to your watchlist by clicking here.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.