As much as I'd like to regularly use DuoCards (even with the premium month I've got for inviting a friend!), I just don't do it.. and keep using Duolingo. most probably because of the well-done gamification, with the 800+ days of streak, daily quests, friends' quests, and even well-timed and well-worded notifications that keep calling you back. I understand, this requires a lot of work and efforts from you, guys, and you can say that truly motivated learners don't need all of that. But hey, if DuoCards had at least some of those gamification techniques.. The current one with the mammoth and its home - it certainly has potential, but for me, it just doesn't work at all. I don't understand it. It's too complicated, and since the "streak" does not go away - it does not motivate me to keep it. And with no reminders - there's little to no chance to build a habit. Again, I won't go into details - you can better talk to some AI about it, but I truly wish you could make an improvement there to actually get a higher engagement and retention rate. Good luck! P.S. if you haven't yet, I highly suggest watching the TED talk of the Duolingo founder, where he talks about gamification and reminders, and the whole competition for the user's time and attention.
