Our take: Facebook shares are down despite Facebook's recent reassurances that the company is doing well. Don Reisinger from CNET explores the different reasons for Facebook's falling shares.

"Facebook shares are down today, spelling some possible erosion in the stock price heading into the rest of the week of trading.

"Shares in the big social network are down 3.5 percent today to $30.13 in early trading. The company's stock ended the day yesterday at $31.24, up significantly from the company's 52-week low of $17.55. That rally has been due to Facebook's ability to gain traction in mobile and reassure investors that it could continue to grow.

"The company went a long way in making its case yesterday, reporting better-than-expected fourth-quarter earnings. During the period, the company's revenue grew 40 percent year over year to $1.59 billion. Facebook was also able to post an adjusted earnings per share of 17 cents, beating Wall Street's estimates.

"So then, why are Facebook shares down? It might have less to do with past performance and more to do with the ability for Facebook shares to actually grow."