Here's the secret of mastering a new language, according to Duolingo CEO Luis Von Ahn (pictured). Luis von Ahn

There's one thing that separates the success stories from the failures when it comes to learning a new language.

That's consistency.

People who practice their language for 15 minutes before bed have a major edge on other Duolingo users, according to founder and CEO of the language learning app Luis Von Ahn.

"Those people we know are going to stick around for a really long time," von Ahn says. "We see them doing that for a week, we say, 'This person is going to be here for a while.'"

Meanwhile, users who binge — spending hours on the site, cramming in French or German or Chinese language lessons — tend to disappear fast.

That's because, no matter what sketchy online ads tell you, learning a language is a marathon, not a sprint. You cannot hope to master a language in weeks — or even months. So people who start out of the gate at full speed tend to burn out fast.

"If you are able to make it a part of your routine and space it out, that's much better than going nuts and cramming," von Ahn says. "It is not a sprint. If you sprint, you will forget everything."

Von Ahn says that he's currently learning Portuguese, and applying the principal of consistent, daily practice to his own learning sessions. So far, it's working out well. He's gotten to the point where he can understand a great deal of it and even watch Portuguese movies.

"When I speak Portuguese, I sound like a combination of an American and a Mexican speaking Portuguese," he tells Business Insider. "I can pretty much understand everything. I know what to say — I just sound really bad."