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 lululemon athletica (LULU 1.47%) were coming up lame today, falling 17% today after the company released a negative update on its fourth-quarter performance.

So what: The yoga-apparel purveyor said it now expects revenue in the range of $513 million to $518 million, with comparable sales in the negative low to mid-single digits, reducing its expectations from sales of $535 million to $540 million on flat same-store sales. It also dropped its EPS projection from a range of $0.78 to a ranger of $0.80 to $0.71 to $0.73. CFO John Currie explained, "We were on track to deliver on our sales and earnings guidance through the month of December; however, since the beginning of January, we have seen traffic and sales decelerate meaningfully." Currie added that the lower guidance was based on the assumption that current trends would continue.  

Now what: While many retailers have reported miserable holiday seasons, Lululemon survived the tough December, but the recent struggles perhaps indicate deeper problems. The company had a tough 2013 that included a massive product recall and the surprise resignation of its CEO, and today's update does nothing to reassure shareholders that 2014 will be any easier. It's hard to say what the culprit is here. The company is facing rising competition, but that shouldn't cause a sudden slowdown in sales as we're seeing. The forecast could be a bit conservative, as the company is getting ready to present at the ICR Xchange conference tomorrow and wants to get bad news out of the way, but negative same-store sales are alarming for a retailer that was once flying so high. Currie said that Lululemon was "starting to see the results of the significant investments we made throughout this past year." The yoga master needs to share those results with investors fast, or else I'd expect the stock to keep sliding.