Luis von Ahn, CEO of Duolingo, shares hard lessons from a viral AI memo that sparked backlash—revealing why AI's quality limitations matter more than hype, and explaining why he's pivoting to user growth over revenue in 2026 to capture billions of learners before ads become inevitable. AI demos well but fails at scale: when Duolingo tried to generate 1,000 stories for language learning, 20% were unusable, forcing the company to prioritize human creativity over speed.