What: Shares of GoPro (NASDAQ:GPRO) fell more than 16% early Thursday after the action camera maker announced weaker-than-expected third-quarter results and light forward guidance.

So what: Quarterly revenue rose 43% year over year to $400.3 million, Driven largely by international strength including 175% combined growth in the EMEA and APAC regions. That translated to a 103.9% increase in adjusted net income to $36.6 million, and a 108.3% jump in adjusted net income per diluted share to $0.25.

By contrast, analysts were anticipating revenue of $433.6 million, and adjusted earnings of $0.29 per share. And that overestimation wasn't a fluke; GoPro's own guidance called for revenue of $430 million to $445 million, and earnings per share of $0.29 to $0.32.

"I am proud of our year-to-date accomplishments in which we posted strong financial results and expanded our portfolio of products," added GoPro CEO Nick Woodman, "however our business in the third quarter was clearly more difficult than anticipated."

To be sure, in light of weak initial sales, GoPro noted it "re-launched" the HERO4 Session camera this quarter -- a reference, of course, to its widely publicized $100 price drop for the now-$299 device. In addition, GoPro believes it may have "underfunded" marketing in Q2 and Q3, negatively impacting demand overall.

Now what: But perhaps most concerning is GoPro's guidance, which calls for fourth-quarter revenue of $500 million to $550 million, representing a year-over-year decline of 17% at the midpoint. Combined with a ramp in spending related to marketing, as well as software and entertainment initiatives, GoPro expects fourth-quarter earnings per share of $0.35 to $0.45. Analysts, for their part, were modeling Q4 revenue and earnings of $690.5 million and $0.82 per share, respectively.

After its guidance for Q3 turned out to be overly optimistic, perhaps GoPro chose to bite the bullet this time and under-promise with the intention of over-delivering. But in the meantime, given this Q4 guidance and its first quarterly miss since going public last year, I can't blame the market for bidding down shares of GoPro today.

Steve Symington has no position in any stocks mentioned. The Motley Fool owns shares of and recommends GoPro. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.