Kevin Systrom, co-founder of Instagram, toiled away on Burbn, one of his early startups, for a while before he realized it just wasn’t going to happen.

“I remember saying that I was just waiting for hockeystick growth. That doesn’t happen. You don’t just sit there, and all of the sudden there’s a lot of growth,” he said at PandoMonthly in San Francisco today.

Hockey stick user adoption, like what he experienced with his next startup, Instagram, came from making a major change. Burbn was intially a check-in and communications app in a sea of a million check-in and communications apps. He realized that the thing he liked most about Burbn was the photos that the app’s 80 other active users shared. He decided to throw all his eggs in that basket, and boom — hockey stick growth.

“We took in data about what our users were doing and focused in on that. The second we focused on what people were doing, it became a phenomenon,” he said.

“That’s something that comes from following what people love. And if you just use psychology a little, and you listen to your users and see what they’re doing… Sometimes, if you just do what they are hinting at what you should do with their behavior, good things can happen,” he said.

Instagram had 25,000 users on its first day. On that day, Systrom knew it was going to be huge. “I’d never seen people fall in love with something so quickly,” he said. Part of that growth was because Instagram didn’t rely on network effects. The app purposely allowed users to share their photos everywhere, on Twitter, Foursquare, and Facebook. One-quarter of all Instagram photos are still shared on those networks, which makes the app useful before users have a network within the app but also drives adoption.