I've been deep in gamification research while building a study app, and it's made me pay way more attention to which non-game apps actually hook me. Duolingo's streaks, Snapchat's snap score, even a habit tracker's little dopamine hit when you check something off, they're all borrowing the same mechanics games have used forever.

Curious what does it for you. Is it a streak you don't want to break, a collection you want to complete, a leaderboard you're quietly competing on? Or something else entirely?