Duolingo built its lessons around short, game-like rewards, and the lesson-complete sound became one of its most recognisable signals for learners finishing a session. As users began recording their streaks, scores, and study routines for social media, the chime travelled beyond the app and started appearing in edits that celebrate progress. It remains popular because it is instantly understood by anyone who has used the app, turning an ordinary completion into a shared, satisfying moment.