Luis von Ahn, the co-founder of Captcha, never cared much about culture. But that was then. He tells Inc.'s Jeremy Quittner that in his new venture--Pittsburgh-based language teacher Duolingo--his priorities are very different.

What is the single most important thing you've learned from your previous businesses?

Having a good co-founder really matters. I put a lot of weight on feelings and am weirdly in touch with them, which is not typical for an engineer. My current co-founder, Severin Hacker, is really logical.

I am in charge of product; he is in charge of technology. I do the specs of what needs to be done, and he figures out the best way technologically to do it. He also thinks bigger than me: If I want to have a $100 million company, Severin wants a $100 billion company.

What else are you doing differently this time around?

I'm spending a lot of effort on team dynamics. Our team at Duolingo is really cohesive, but this did not just happen. I made a concerted effort to hire people who are going to play nice.

In the past, I just looked at how competent people were, but it sometimes happens the most competent are the biggest assholes. I used to think this does not matter, but I realized this is really important.

Do you take a hands-on approach with the hiring now?

I do. Every person that comes through here, I talk to them for an hour. It is amazing how much comes out in an interview.

You sold your two previous companies. Is that your goal with Duolingo?

I just did what made sense at the time. And I would say that right now it does not make sense for us to sell to anybody. The product is pretty successful, and it is growing, and there's nobody we see as a clear partner. I've made enough money. What's important now is to have a positive impact on people.

Duolingo is backed by some brand-name investors, including Ashton Kutcher and Timothy Ferriss. What have you learned about dealing with the money guys?

This is the first time I've had VC backing, but I've learned a lot. Before, I didn't know that on a Series A round of funding, you sell around 20 percent of the company. So if someone comes around and proposes 40 percent, you know that is not right.

The other one is boneheadedly simple: Competition among investors is good. If you are talking to one big VC and wind up talking to another, they will find out. How much that matters is insane.