Show HN: A retention mechanic for learning that isn't Duolingo manipulation?

I've spent the last few years shipping learning products at scale - Andrew Ng's AI upskilling platform, my MIT Media Lab spinoff focused on AI coaching. the retention problem was the same everywhere. people would engage with content once and not return. not because the content was bad - rather because there was no mechanism/motivation to make it a habit. the standard industry answer is gamification - streaks, points, badges. Duolingo has shown this works for language. but I'm skeptical it generalizes.