I don't think GoPro went down because of the threat of the patent. Rather, investors are afraid Apple will start to compete against GoPro. People are seeing the patent as a possible product roadmap not a legal threat.
I have no idea if GoPro stock is overvalued, undervalued, or just right. But I will say that they've had a really nice run with a product that IMO is not all that great (terrible UI among other things) by plugging themselves into the adventure sports lifestyle. And, probably more importantly, those who like to think of themselves as being part of the adventure sports lifestyle--whether they do or not.
I've always been surprised GoPro are as popular as they are.
Before GoPro was even a known brand you could easily buy extremely similar items (small plastic cameras with one-two button(s)) off of eBay straight from China which cost under $50. They often came with generic stick on clips for motorcycle helmets and similar.
This entire market existed for years before GoPro suddenly appeared. All GoPro did was package up the generic product from China, increased the price by 100%, and then used all the extra revenue to buy a ton of adverts.
People often like to claim that GoPro won because it was optically better, but that just isn't accurate. Up until maybe the HERO3+/HERO4 (2013/2014) the line was actually quite behind some generics. The only reason GoPro even got their act together was that some other named vendors started getting into the "action camera" market.
Even today GoPro seems insanely expensive, for the price of a single GoPro HERO4 SILVER[0] with a basic plastic case you can buy the same spec camera on eBay for $65 [1] with enough money left over for a [bad] DSLR by Canon/Nikon/Sony/etc [2].
>> People always seem to know why stocks move - after they have moved.
Hindsight is perfect, you just get all the survey results from the buyers and sellers and see what the common reasons for buying/selling were. Then you post an article before the closing bell that same day. Easy.
People think they know why they do what they do. But when you try and encode it, it fails.
I've worked with traders, trying to implement the system they think they use. They had a system of indicators and said they traded according to them but when applied mechanically to trading data it didn't make a profit.
maybe it's difficult to uncover the opposite story, but when was the last time we heard a story like: "Large corporation stock price drops because small tech company was awarded patent".