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 Barnes & Noble (NYSE:BKS) were heading to the bottom shelf today, falling as much as 13% after its chairman sold a significant stake in the company. 

So what: The bookseller announced today that chairman and founder Leonard Riggio had sold 3.7 million shares, or approximately 6% of shares outstanding, worth around $70 million. Riggio remained Barnes & Noble's largest shareholder after the sale, holding about 20% of shares outstanding, and said he feels "very good" about being the company's largest shareholder. He added, "I love this company and I believe in its future as I do in all of the wonderful people who work here." Riggio also said that he has no plans to sell any more stock this calendar year. 

Now what: Insider buying and selling often moves tickers, but considering Riggio held on to the majority of his stake, I don't see today's news as being significant. Barnes & Noble shares tumbled earlier this month after Liberty Media sold 90% of its stake in the retailer, which was seen as a reflection of the Nook's failure to turn profitable. The two major sales coming so close together may make investors jittery, but the company's sliding sales and continuing losses in the face of online competition should be the real focus of investor concerns.

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.