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 E Commerce China DangDang Inc (NYSE:DANG) were getting banged up today, falling as much as 21% after coming up short on the top line in its first-quarter earnings report. 

So what: The Chinese online retailer posted earnings of $0.01 per share, better than estimates at break even; but revenue growth of 30%, to $279.2, million missed as analysts had expected $285.6 million. CEO Peggy Yu Yu said the company continued to make "good progress in transforming Dangdang from an online bookstore into an integrated online shopping mall," and it "continued on its path to profitability." 

Now what: Guidance for the current quarter was also a bit weak, as Dangdang sees revenue of $311 million against expectations of $320.2 million. Dangdang's stock got punished also because peer Vipshop Holdings soared after its earnings report came out, and because the stock had been bid up significantly during he week, gaining 13% before today's fall. A downgrade from Bank of America to Neutral also weighed on the stock, as B of A sees increasing competition and declining revenue per customer as headwinds for the company. Still, the overall growth story remains intact. I wouldn't get too worked up about today's sell-off.

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.