https://techcrunch.com/2021/05/08/how-duolingo-became-a-2-4b-language-unicorn/

At the heart of Duolingo is its mission: to scale free education and increase income potential through language learning. However, the same mission that has helped it grow to a business valued at $2.4 billion with over 500 million registered learners, has led to tensions that continue to define the business.

How do you survive as a startup if you don’t want to charge users? How do you design a startup that isn’t too hard to lose people, but isn’t too easy to compromise education? How do you balance monetization goals while also keeping education as a product free?