They promise "free, fun, effective" learning, but their mascot literally threatens you with death memes when you skip a lesson. | They had to steal tricks from FarmVille to make people care about conjugating French verbs — that's not product-market fit, that's digital manipulation. | When your growth engine breaks, you're left with an owl making threats to teenagers.

Sources from Lenny's Newsletter and Podcast: How to win in consumer subscription (Newsletter), How Duolingo reignited user growth (Newsletter), The Subscription Value Loop: A framework for growing consumer subscription businesses (Newsletter), How to increase your product's retention (Newsletter)