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. duolingo's retention is built on a very specific anxiety loop that feels increasingly manipulative and doesn't translate well to topics like astrophysics or reading dense research papers.

i've been building Daily - 5 min/day structured social learning on any topic, personalized by knowledge level. Eerly and small (20 users). the interesting design question i keep running into: what actually drives someone to return to learn something they want to learn but don't need to learn? no external accountability, no credential at the end, no job pressure. pure intrinsic motivation is notoriously hard to sustain.

my current hypothesis: the return trigger isn't gamification, it's social - knowing someone else is learning the same thing, or that someone will notice if you stop. testing this in month 1.

has anyone built in this space or thought carefully about the retention mechanic for purely intrinsic learning? curious what the HN crowd has seen work.