I’m trying to learn French with the help of Duolingo.
Duolingo has done the work of knowing what business it is in, and its not Language Education. Its Resolution Keeping. It knows its business intimately and evidently invests in building an experience to help its users keep their resolve.
Duolingo is successful because it makes the end user successful. It has many features but two stand out in doing this:
1. The Streak - the numbers of days you’ve consistently practiced. With a streak there is no wiggle room. Either you practiced or you didn't and nothing is more motivating then keeping your days-in-a-row count from going back to a very depressing "0".
2. Achievable streak-maintenance. In order to get a day’s practice to count, you must complete a lesson. Lessons are short, Duolingo access is everywhere.
This is an example of user-centric business and design. They will continue to succeed because its end user's do.