Despite slow initial growth, Silbermann told the crowd why he never gave up on the startup.

As a child, Silbermann enjoyed collecting things, from insects to stamps.  "What you collect says so much about who you are," he mused.  Pinterest was built to help people continue their collections online.

After nine months, Silbermann said the site had less than 10,000 users and many weren't using it daily.  "I sent Pinterest to 200 of my friends and I think 100 of them opened the email. It was catastrophically small numbers,"

"I included a lot of people from Google and California, and I emailed a lot of people from Iowa.  The people who started using it used it the way we had hoped. I think those few people kept Pinterest going."

Silbermann personally contacted the first 5,000 users. He has given many of them his cell phone number and continues to communicate with them.

When asked why he didn't give up during the tough first year, Silbermann said, "The idea of telling everyone we blew it was so embarrassing. I thought, 'Google is never going to take me back -- they barely hired me the first time!'"

"To me boards are a very human way of looking at the world," said Silbermann, who admitted he sees the world as a series of people's collections. He even referred to his wife's closet as a collection of shoes and clothes.

Not everyone loved Pinterest's grid-like design though.  Most of the world was caught up with real time feeds and text when Pinterest launched.

Eventually, the site started to catch on but Silbermann says Pinterest wasn't an overnight success -- no actor signed up and brought in a flood of people.