Ask Luis Von Ahn why he decided to become an entrepreneur and he will tell you that the career actually chose him. When he was a professor at Carnegie Mellon in 2005, he developed a program that websites could use to distinguish humans from robots. CAPTCHA became so popular that school officials urged Von Ahn to turn the program into something more.
"At some point the university was kicking the project out because it had too many users and they just said, 'You can't be in the university, you have to do something about it,'" he says. "I had to turn it into a company."
In 2006, he received a prestigious six-figure MacArthur Fellowship, otherwise known as the "Genius Grant," which also recognized his work with CAPTCHA. In 2011, when, the entrepreneur estimates, his CAPTCHA system was digitizing two-and-a-half million books a year, he launched his new initiative, the free tool for language learners, Duolingo.
Though he never planned for entrepreneurship to be his career path, Von Ahn does appreciate the fortuity. He came from a family of business people. In Guatemala, his parents owned one of the largest candy producers in the country, Tropical Candy.
Today, there are 1.2 billion people around the world learning a new language and 150 million of them, aged seven to 95, are now using Von Ahn's website Duolingo to do that learning for free.
But reaching this milestone has been no easy feat. Here are some of the challenges Von Ahn has needed to overcome.
1. Growing a following
In April 2011, Von Ahn gave a TED talk about how collaboration online could be used for the greater good. He recounted how CAPTCHA has helped digitize books and how he hoped to use his Duolingo to help millions of people learn a new language at no cost.
"That talk got watched by two million people," he says, "and that was luck that it coincided [with the company's launch]."
As the company continues to launch new features, he hopes to attract even more followers, but he says that's one of the most difficult parts of growing his company: Getting, and retaining, an audience.
2. Managing from within
Prior to becoming a job creator himself, Von Ahn didn't give much thought to how companies like Google treated their employees. But as his company continued to grow, he realized it was crucial to keep his company organized and his workers happy.
"I hadn't thought to spend time on how to organize all the people," he says.
Proper management has become increasingly important at Duolingo.
3. Hiring the right people
As most companies do, Duolingo started small.
Perhaps one of the biggest mistakes that Von Ahn says he made early on was making the wrong hires, and choosing inexperienced people. Employees were expected to assume different roles and recent graduates were tapped even though they sometimes lacked the proper background for their roles.
Ultimately, he learned that choosing individuals with the right experiences and skills was crucial.
Making mistakes, the entrepreneur says, is the way that he gained the skills he needed to grow the company. And Duolingo does keep expanding, as well as launching new features. Its latest? Chat bots to help users practice a new language using artificial intelligence.
This post originally appeared on CNBC.com.