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's happening
Shares of GoPro (NASDAQ:GPRO) were down 13% just before market close on Friday despite a better-than-expected fourth-quarter report from the action camera specialist.

Quarterly revenue rose 75.4% year over year to $633.9 million, which translated to adjusted earnings per diluted share of $0.99. Analysts, on average, only expected earnings of $0.70 per share on sales of $580.3 million.

Why it's happening
During the quarterly conference call, however, GoPro management said it expects current-quarter revenue of between $330 million and $340 million, representing growth of 42% at the midpoint. And primarily given continued investments in research and development -- expenses that almost doubled on a year-over-year basis in the fourth quarter, to $46.1 million -- GoPro anticipates first-quarter earnings per share of $0.15 to $0.17. By contrast, while Wall Street only modeled revenue of $324.8 million in the quarter, it was looking for earnings at the higher end of GoPro's expected range.

Separately, GoPro revealed in an SEC filing that Chief Operating Officer Nina Richardson tendered her resignation on Feb. 2, to be effective as of Feb. 27. During the conference call, both GoPro CEO Nicholas Woodman and Richardson herself insisted her three-year stint is ending on good terms. According to Woodman, now that Richardson has helped GoPro successfully scale its operations in product development, she's leaving "to pursue board roles and other opportunities."

In the end, perhaps the market expected more in the first quarter from GoPro, which has also yet to recognize meaningful revenue from its impending transition to a "media" company. But all things considered -- and keeping in mind it crushed even its own expectations in the fourth quarter -- I'm encouraged that GoPro's core market appears to be as strong as ever.