* Positive reinforcement: cheerful noises and visual progress once I completed a section.
* Negative reinforcement: if I didn't practice at all that day, I would get a notification at 11pm. If I ignored for a while, they were super passive aggressive, saying things like "These don't seem to be working. We'll stop sending them". I felt guilty and would start agin.
* I wanted to keep my daily streak going. It made me feel like Jerry Seinfeld with his "write a joke a day; put an X on the calendar" technique.
* I liked the concepts of experience (exp) and levels; it let me feel like I was making concrete progress, even if I was totally incompetent. I indulged my gamer side while still being productive!
* duolingo works just as well on browser as mobile
* Training sessions were short enough that if I only had a few minutes of downtime, as long as I had my phone on me, I could actually be productive. This made subway rides that much better.
* duoolingo offers a practice mode where I could work specifically on my speed if I had longer chunks of time and wanted to dive deeper.
And today, I can totally speak intelligible Swedish [1]. It worked.
[1] https://www.youtube.com/watch?v=OxoXe5FDIkA – some phrases are off (I should've said "hur man sköter marknadsföring själv") and pronunciation is off.