Ben Silbermann, the founder of Pinterest, navigated a roundabout path to founding a technology company. Until his junior year of college, he expected to go to medical school.

“My parents are doctors, both my sisters are doctors, so I figured I'd just be a doctor too,” he said. “Sometime in my junior year I had this sudden realization that maybe that wasn't for me. I was sort of lost at sea.”

Upon graduating college in 2003, he took a consulting job in Washington, D.C.. He started reading tech blogs, and became fascinated with the second Silicon Valley start-up boom. He says he felt that it was “a story of my time that I had no part in.”

So begins the story of Pinterest. Silbermann explained to an audience of hundreds at the annual South by Southwest Interactive conference in Austin, Texas, how he created the super-popular social-bulletin board site. It was a highly anticipated talk not only due to Pinterest's recently skyrocketing user growth—and its astronomical new $200 million valuation—but also due to the fact Silbermann has been generally silent to the press.

In his talk, he nodded to that fact by saying that, despite tech and entrepreneurship sites inspiring him to start his company: “I think at any given moment, just by personality, we'd rather be working on the product than doing interviews. There was this vacuum of news, and a few months ago it all really broke at the same time.”

And that, Silbermann said, felt like a "really weird phenomenon" to him.

“It's exciting to see people using the product in ways that we never really expected. It's exciting that people care a lot. And then you also feel this weight of responsibility, you sort of brought this little thing to the world, this little product, and you want to see it get better,” he said, nodding to the fact his company is building out new features at a rapid clip. “I think anyone who makes products has this simultaneous joy and, almost, shame looking at it. You look at it all day and all you can see is all these things you want to make better.”

Pinterest is a social website on which users post images of various items—from a hairstyle to a motorcycle—to boards that function like image folders. Users can “re-pin” items they like from others' boards to their own, comment, or simply “like” pins. The well designed site is the eye candy of social media, and is gaining reputation as a traffic referrer more powerful than LinkedIn or Google+—and one with a more natural connection to retail stores and items.

In late 2011, Pinterest cracked the list of the top-10 social networks globally. Silbermann and his two co-founders have nailed down $37.5 million in funding, for a valuation of $200 million.

How'd that happen? Rewind to 2003, when Silbermann was reading the tech blogs. It was around that time he quit his consulting gig, moved to California, met co-founder Paul Sciarra (with whom he made iPhone apps), and started knocking on Google's door to learn the Silicon Valley ropes.

“I didn't have an engineering background, so I really had to cajole my way into Google,” Silbermann said.

He admired Google for its innovative attitude about product-creating. “They really had this audacity to think on a huge scale....Google was like the only company that was like, we're making so much money, let's take a picture of every street in the world. Nobody does that.”

“For me, Google was the coolest place. It was the coolest place,” he said. In the time he worked at Google, fellow Google employees included Kevin Systrom, who went on to found Instagram, and the creator of Foursquare, Dennis Crowley. “People there were so smart. And they were all doing these really interesting things. I just felt lucky to be part of it even in a small way.”

Pinterest started in 2009 as a night-and-weekend project. As a kid, Silbermann said, he collected lots of things, such as insects and stamps. As an adult, he began to think that the things we collect can say a lot about who we are and what we are interested in.

“I can't say it  came from really hard-nosed business analysis,” he said. “It was just something I really wanted to see built. I just thought it could just be so good for the world if you could just share these things about themselves.”

It started with a small idea: How do we best share things with three or 10 people or 20 people? Silbermann says his small team never thought about what kind of sharing system would work for a million people—only what would work for a small network. Design was their big focus. The team debated over every detail a user sees on Pinterest today: should there be boards? Repinning? A concept of a feeds? Should it be links or items?

“There were literally dozens of version that [Pinterest grid] were fully coded, fully styled with live production of data that we went through” he said. “We'd vary the width, we'd vary where the meta-data was, we'd vary was the person on the left side or the right side...We just felt like if your collections didn't look awesome, if they weren't really beautiful, why would you spend time to build them?”

After seven months of working on Pinterest, Silbermann said he sent an email to 200 friends inviting them to use it. “I think of them 100 opened the email, which I think said something,” he said.

“I was like catastrophically small numbers,” he said. And the user-base grew super slowly. After nine months, Pinterest was still under 10,000 users, and a lot of them weren't using it every day. Why didn't he quit?

“The idea of telling everyone that we blew it was just so embarrassing,” Silbermann said. “I was like, Google barely hired me the first time, I'm never going to get back in.”

Seriously, though: “We just felt like if everyday we were getting a little bit closer to something that we would be really proud of, we would never regret the time we'd invested,” he said.

Looking back today at what he learned early on in building the business, Silbermann said he has some lessons to share with aspiring entrepreneurs.

“Don't take too much advice,” he said. “It's just that most people who have a lot of advice to give—there are a few people who are exceptions, and they have a lot of data in front of them—most people generalize whatever they did and say that's the strategy that made it work.”

Silbermann prefers a “what-if?” attitude.

“People say, was it that Pinterest was invite only the secret to its success?” he said. “I don't know! Maybe it'd be 10 times bigger a year ago had it not.”