What: Shares of GoPro (NASDAQ:GPRO) fell 19.9% in October, according to S&P Capital IQ data, driven by the action-camera maker's weaker-than-expected third-quarter results. As it stands today, that leaves GoPro stock down a harrowing 59% year to date:

GPRO data by YCharts

So what: GoPro's results looked encouraging at first glance; third-quarter revenue rose 43% year over year to $400.3 million, while adjusted net income more than doubled to $36.6 million, or $0.25 per share.

Unfortunately, only three months earlier GoPro had told investors to expect significantly higher revenue of $430 million to $445 million, and earnings per share in the range of $0.29 to $0.32. Those results also fell short of Wall Street's expectations, which had predicted that revenue and earnings would come in at the low end of GoPro's guidance.

In part, Wall Street's pessimism stemmed from an admission by GoPro management a few weeks earlier that their new HERO4 Session camera wasn't selling as well as expected with a suggested retail price of $399 -- a consequence of continued high demand for GoPro's higher-end (and similarly priced) HERO4 Black and Silver models. In addition, GoPro believes its underfunded marketing in the second and third quarters hurt demand for all of its products. 

Now what: To combat weak sell-through and in response to "strong feedback" from consumers, GoPro first reduced the price of the HERO4 Session by $100 to a "more accessible" $299. In addition, the company opted to ramp up marketing to revitalize demand forward, including a return to television for the first time since last year.

Even so, GoPro also offered new guidance for revenue in the crucial holiday season of $500 million to $550 million, or a decline of 17% year over year, while earnings should decline to a per-share range of $0.35 to $0.45, down from $0.99 in the same year-ago period. Analysts were much more optimistic going into the report, as consensus estimates predicted fourth-quarter revenue and earnings of $690.5 million and $0.82 per share, respectively.

But there is a silver lining: Patient investors can still look forward to an inevitable refresh of GoPro's core camera product line in the coming year, and GoPro is still on track for first-half 2016 launch of its new differentiated quadcopter solution. And that's not to mention GoPro's longer-term efforts to become a media powerhouse, notably as a content provider in the burgeoning virtual-reality space. So in the end, while it's painful to endure a drop of this magnitude over such a short duration, I'm not convinced long-term GoPro investors should be losing sleep over this short-term movement.

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.