Sometimes, things go viral: The Dress, the llamas, the Ice Bucket Challenge, the How Old Do I Look? app, and so on. One can’t fault companies for trying to figure out how to go viral and gain huge exposure.

But many marketers don’t quite understand how to predictably trigger virality.

“It’s a bit like product-market fit — you know when you hit it, but you don’t know you get there till you get there,” Joe Braidwood, chief marketing officer of SwiftKey, said today during a panel discussion on growth hacking — that analytics-oriented, social-focused approach to startup marketing — at VentureBeat’s 2015 MobileBeat conference.

A few weeks ago, SwiftKey ended up on the font page of discussion board website Reddit, resulting in 32,000 comments.

“That’s viral,” he said. “You can’t engineer it. It just happens.”

Despite Braidwood’s uncertainty on the matter, a couple of his fellow panelists did have a few ideas about how to prompt something to take off, and how to make the most of it. Which is useful for any startup looking to build a following.

For one thing, some messages might be more likely to go viral than others, depending on how they make people feel.

“Things that make them feel loved more, make more money, feel smarter — those are the units you need to type into your system to allow people to share,” said Manish Chandra, founder and chief executive of Poshmark. “It’s really looking at what is going to make that person feel better.”

And rather than sharing something that advances a company’s agenda, people share “to propagate their own agenda,” Chandra said.

But companies can also learn from the day-to-day word-of-mouth discussion about their products. The people at TrueCaller noticed that Uber app users have been using the TrueCaller app to verify the identity of drivers, said Tom Hsieh, vice president of growth and partnerships at the startup.

And so, as a result, Hsieh said, the startup is keen on doing marketing campaigns around safety and verifying identities.

“I’d say that manufactured virality — it’s really tough,” said Terence Fung, chief strategy officer of Storm8. The ability to spam everyone in the address book of a new user’s smartphone has largely been “closed off,” Fung said.

With that said, companies can pay careful attention to the social networks where their content does take off.

It’s about “reverse engineering why you’re achieving some of those numbers — and then try to accelerate that,” Fung said.