Instagram's numbers are staggering: 400 million active users each month; 80 million photos that garner 1.2 billion likes per day. Wild metrics for any company, but especially crazy when you consider the social media company is just over five years old. But what has made Instagram the clear winner in a crowded field of photo sharing apps?

Co-founder Mike Krieger thinks it might be because the company has a habit of doing things in a counterintuitive way. "We like to flip assumptions," Krieger told a crowd in New York on March 11 during the 7 Days of Genius festival. While building the app, for example, Krieger and fellow co-founder Kevin Systrom discussed a common belief: "People want to share photos with only their friends and loved ones." Then they decided to operate from a different assumption: "People want to share their photos publicly with lots of people." That concept became the driving force behind Instagram. 

Likewise, it's easy to fall back on plenty of built-in assumptions when you're starting a tech company, especially in Silicon Valley. Krieger and Systrom willfully ignored some of the biggest assumptions. Here are four surprising ways the co-founders have built Instagram into the social media behemoth it is today.

1) They take their time building new features. LinkedIn founder Reid Hoffman said, "If you're not embarrassed by the first version of your product, you've launched too late." Facebook, which purchased Instagram in 2012, long held the mantra "Move fast and break things." Instagram's philosophy is different. While Facebook is known for testing changes on small percentages of its user base, Krieger and company prefer to get new elements as close to perfect as possible before rolling them out. They build the features behind the scenes, then test them on colleagues and friends. "We want a cohesive experience for our users," Krieger says. 

2) Their goal is to have people spend as little time using the app as possible. Krieger remembers, in the days before Instagram, being at a concert and seeing people in the front row snap photos of the band--and then wait with their phones out while the photo uploaded. Instagram focuses on making the app move smoothly and quickly. "Life is what you should be experiencing," he says. "Not a progress bar." 

That philosophy extends beyond load times. The filter icons on Instagram's interface used to offer an intentionally blurry preview of what the photo would look like. When a colleague suggested that making the image sharper would help users make faster decisions on what filter to choose, Krieger and the team made the change. "The only metric it moved was time spent on the app," he says. "But that's worthwhile. You can finish posting and resume your life."

3) They want to give users as few options as they can. Krieger knows this is how most people use Instagram: They're waiting for a bus or train, and they whip their phone out and click the app for a brief look at what's been posted. More options would alter that experience. Instagram's developers have two lists: projects they're working on, and projects they decided to scrap before even beginning. The vast majority fall into the latter category. "We prefer to make each section better instead of making Instagram wider," Krieger says. "Do fewer things better." Lots of websites and apps feature the icon known as the "hamburger," three parallel horizontal dashes usually at the top corner of an app or website. When clicked, the icon expands out into a larger menu. "If we ever have that," Krieger says, "we've blown it."

4) They don't try to know everything. Krieger and Systrom weren't photography experts when they started Instagram, nor were they master developers. But their lack of expertise helped them keep an open mind and approach the app from the consumer's perspective. "Our ignorance was powerful" Krieger says. "If we had known any more, we would've screwed it up."