I'll start. I used to love Duolingo. Until I didn't. And as a Product Manager, I perfectly recognized their strategies. They have great retention rates and all that but they didn't retain me. I sent them customer fedback more often then I can remember, but death silence. ​ What annoys me? Well you can't actually move past certain point. Like you have learned it, perfectly, and went a step ahead, and another one, and another two. And it keeps pulling me down to the step 0. I am so sick...