Updated January 20 to correct Slack’s history. Butterfield only started one gaming company after Flickr, not two as previously reported. And Slack evolved from an internal communication tool, not a feature of the game. 

We already knew that corporate messaging app Slack was one of the hottest startups around. What we didn’t necessarily know was why.

As it turns out, Slack founder Stewart Butterfield isn’t so sure himself. Speaking on stage at the Digital Life Design conference in Munich, Germany, Butterfield said he didn’t know why Slack had taken off while his last two startups had fizzled.

“I get in trouble with my PR team for saying this,” he said. “But I have no fucking idea.”

Butterfield, of course, is perhaps best known as a cofounder of Flickr, which evolved from a gaming company he started and was sold to Yahoo. After that, he started another gaming company that pretty much went nowhere. But this second gaming company had created an internal chat tool that became the kernel of Slack.

So, as moderator Jochen Wegner said, Butterfield has become the “poster boy of pivots.”

Of course, Butterfield did have some theories about why Slack is booming. In general, he said, enterprise software is a mess and a field of huge opportunities. And while it seems like chat has been around forever, he said, mobile and cloud services are creating new openings for new services like Slack to be more useful to a wider array of employees and businesses.

“The time is right for this kind of product,” he said.

Back in October, Slack raised $120 million in a round led by Google Ventures and Kleiner Perkins. The company has raised $180 million total, and the latest round gave it a valuation of $1.12 billion.

At the time, Slack said it had “30,000+ active teams using Slack” and 268,000 daily active users. It also said its active user base is growing by 3 to 5 percent a week.

How’s that growth looking since then? Butterfield didn’t reveal numbers, but he did show this chart:

slackchart

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