'Failing' in what sense?
Stock down more than 70% year-to-date, and competing in a market that is rapidly becoming commoditized.
Perhaps "failing" is a a strong word, but I wouldn't describe them more positively than "struggling." Like GoPro, Fitbit sells commodity hardware and is not greatly differentiated from its competitors in terms of hardware, software, or platform lock-in (you may disagree, but the consumer market has clearly spoken).
The 30% fall was mainly triggered by Fitbit revising revenue estimates for Q4 from 985M to somewhere around 725M as well as Q3 performing poorer than expected.
What's fascinating is that Fitbit is still going to do about 2.2B in revenue (up from 1.8B) last year. So annual revenue is going to be more than current market cap (1.7B).
Apart from a less than delightful user experience (resulting in device abandonment and low engagement/retention), Fitbit is also losing market share to Xiaomi in Asia.
So I wouldn't call it failing, but yeah it could do much better :)
I don't just mean that. I mean that anybody with business contacts in China could make equivalent fitness-tracking hardware. The barrier to entry for new competitors is very low.
Fitbit needs to be able to prevent a bunch of new competitors from coming out of the woodwork and stealing their marketshare.