Snapchat just might become the world’s third most highly valued start-up, coming up behind Xiaomi and Uber. News broke last week that the instant messaging service, whose content disappears within seconds, is seeking a valuation that could go up to $19 billion.

What makes Snapchat worth that much money? For one, it just launched a new feature called Discover. It’s made up of several channels, via which Vice, CNN, National Geographic and others will broadcast content according to deals they signed with Snaphat.

“They all want to reach Snapchat users who are young, they are millennials, they are the cool kids,” says Will Oremus, a senior tech writer at Slate, who has written about how the app often confuses him.

“We are confounded by snapchat, the little buttons don’t make any sense,” he says.

A self-proclaimed “oldster,” Oremus, 32, says he is 148 in “Snapchat years.” And this, he thinks, is at the heart of Snapchat’s success. It appeals to teenagers and millennials because older people don’t use it. And they don’t use it because it’s confusing, according to Oremus.

Take Facebook, for instance. When it first launched, Oremus says, it was popular among college-going kids because it took some time to figure out and it was largely used by youngsters. Using Facebook effortlessly, and constantly sharing on it, was part of a secret knowledge they shared. But soon people of all ages started using Facebook. Today, Facebook, according to Oremus, is for “the uncool kids and, more than that, for the uncool parents.”

Oremus says this is similar to a theory put forward by venture capitalist Andrew Parker in his blog. In that post, Parker talks about “the secret knowledge culture of gaming,” and how each game came with its own set of cheat codes, passwords and “hidden artifacts.” He writes that this turned the “secret knowledge” into a “shared experience.”

“Snapchat, in its way, is about secret knowledge, too,” says Oremus. “It’s cool because the parents can’t figure it out. The way the kids figure out is they show each other. That’s what makes it fun.”