Duolingo gave a hospitalized 10-year-old his 301-day streak back, then told a guy who lost his 4-day streak to a hangover to get out of their page. Both replies run the same strategy, and Duolingo explained it to Wall Street last week. The streak is the most valuable asset the company owns. Over half of Duolingo's 58.7 million daily users hold a streak of 7 days or longer, and those users are 2.4x more likely to come back tomorrow. Roughly 10 million people have streaks over a full year.…