By Seth Fiegerman, CNN Business

(CNN) -- The team at Pinterest was nervous.

For most of its early history, the digital scrapbooking service had grown unimaginably fast. Millions flocked to it in 2011 and 2012, despite minimal coverage in the tech press. Pinterest grew so quickly that its small team of engineers raced to keep the site up and running, fixing outages on street corners, at coffee shops and, in at least one case, on a paddle boat.

It was the kind of momentum that felt like destiny. "We'd come to Silicon Valley — the California Gold Rush — hoping to hit something big," said Marty Weiner, a member of Pinterest's founding team. "This, I felt like I've hit this thing. This could be the thing that lets me retire."

"This is going to be the new Facebook. A billion users," thought Ryan Probasco, an early engineer at Pinterest.

But by 2013, the stampede of new users started to slow noticeably. Pinterest set up war rooms where employees spent hours poring over data to understand the cause of the slowdown and what they could do to address it. Even today, people who worked at Pinterest during that period seem to have a different answer for why growth began to lag: the rise of Instagram, the struggle to attract men, or maybe just the limits of the word-of-mouth marketing that had worked in its first years.

Mark Zuckerberg had a different opinion. In Pinterest's early days, when the service was still growing at a fast clip, the Facebook CEO told one of his employees that he thought Pinterest was interesting, but "niche," according to a source with knowledge of the conversation. To Zuckerberg, niche meant it would end up with 200 million to 300 million users. So far, he's right. (Facebook declined to comment for this story.)

Pinterest could have attempted to prove Zuckerberg wrong by racing to roll out new features and supplementary services, or perhaps spending large sums to acquire buzzy startups and new users. Instead, Pinterest's leadership chose to move slower and more deliberately in stark contrast to Facebook's move fast and break things mantra, according to interviews with nearly a dozen former Pinterest employees and people close to the company, many of whom spoke with CNN Business on condition of anonymity.

Remarkably, it has put Pinterest's brand in a stronger position today, but not entirely for reasons the company could have predicted.

Pinterest has its moment

For years, Silicon Valley lionized companies that grew fast and asked for forgiveness instead of permission. Now the industry is facing a moment of reckoning over how these same companies are run.

Facebook, the benchmark for success with billions of users and a hugely profitable business, is now under fire for an inability to adequately protect its massive platform. Uber became the most valuable US startup, only to be upended by its own brash culture and growth-at-all-costs ethos. It has since steadied itself, but only after a dramatic executive upheaval, including the ouster of co-founder and CEO Travis Kalanick. And a number of so-called unicorns, including Uber, Lyft and WeWork, are either going public or advancing toward that goal with unprecedented losses of nearly $1 billion or more a year, which have raised concerns among industry watchers.

Against this backdrop, Pinterest is expected to make its Wall Street debut on the New York Stock Exchange this month. The reception to Pinterest's public offering could signal how much investor appetite there really is for a technology company that follows a more cautious playbook.

Pinterest resisted throwing money at its problems, debated product tweaks extensively and did not rush to copy features that helped larger competitors achieve viral growth, employees said. Fond of touting itself as an anti-social media platform, Pinterest never introduced live-streaming or standalone messaging apps, nor did it become a primary hub for news. These features attracted press and users for other companies, but were also later abused by bad actors.

"The company is not flashy and doesn't try to generate a lot of buzz or press for every little thing it does," said Kamran Ansari, former head of corporate development at Pinterest. "It doesn't get some of the notoriety, but I think the term that comes to mind is: built to last." Pinterest's goal, he added, was "building a meaningful business that's going to be sustainable."

At times, however, this culture resulted in product tweaks being debated to death, bordering on indecision. Pinterest underinvested in certain key products, like its advertising technology, which may have jeopardized its initial traction with marketers. And it was overshadowed in the press by newer, flashier platforms like Snapchat. In the words of one former Pinterest employee, moving slower was both a "virtue" and something that likely "destroyed value" for the company.

Pinterest declined to comment on this story.

The company's IPO prospectus, filed in March, hints at the tensions of this strategy. Pinterest generated more than $750 million in revenue for 2018 — an increase of 60% from the prior year — while shrinking its losses to $63 million, which practically rounds up to profitability compared to Uber's $1.8 billion loss in the same year. In fact, Pinterest was in the black in the fourth quarter. But its audience size and engagement remain well behind many of the companies it cites as competitors.

Pinterest has more than 250 million monthly users, barely a tenth of Facebook's user base and precisely what Zuckerberg predicted years earlier. Unlike Facebook, Snapchat and Twitter, Pinterest chose not to disclose its number of daily active users and said that it does "not anticipate that most of our users" will use the service on a daily basis.

The smaller audience is both a boon and a burden. It could hurt Pinterest on Wall Street, where investors have hammered Twitter and Snapchat for user growth that falls far below the lofty standards set by Facebook. But being smaller also gives Pinterest the luxury of being more thoughtful in its approach to protecting the platform. "The scale makes a huge difference," said Kate Klonick, a law professor at Yale who researches the technology sector and is close to members of Pinterest's content moderation team. "They don't have the type of scrutiny on them that Facebook does."

Today, Pinterest's CMO is pitching the service as "one of the truly positive corners of the Internet." That reputation was burnished in February by its bold attempt to combat vaccine misinformation on its platform. Pinterest blocked searches on the platform related to vaccinations in order to curb the spread of anti-vaxx content. Other social media sites have since stumbled to tackle the problem. The perception of Pinterest as a safe haven could help the company as it goes public. Marketers and users are eagerly searching for a less toxic alternative to the Facebook-Google duopoly that dominates digital media.

"This is a case where you're going to have people rooting for it," said Andrew Lipsman, an analyst at eMarketer who tracks Pinterest. Klonick likens the Pinterest story to The Tortoise and The Hare. "They kind of crept along. They just kept going. Maybe they'll eventually win the race, or provide a different model [for success]."

An under-the-radar success story

From the start, Pinterest was a service built by and for people outside the Bay Area bubble. Ben Silbermann, the co-founder and CEO, grew up in Iowa, raised by parents who were doctors, with visions of becoming a doctor himself. When he did take a job in San Francisco, it wasn't a technical role but rather handling customer support issues at Google.

In 2010, Silbermann launched Pinterest with two co-founders, Evan Sharp and Paul Sciarra. After a slow first few months, Pinterest took off — not with the usual tastemakers and early adopters, but with a demographic often ignored by the tech industry: women. Specifically, women in flyover states, looking to bookmark recipes and items to purchase. This dynamic hasn't really changed in nine years. In its filing to go public, Pinterest said that two-thirds of its user base today are women. More than that, it claimed its audience includes "eight out of 10 moms" in the US.

Silbermann held meetup events, personally took customer calls and visited Apple stores to "change all the computers to say Pinterest," according to one talk he gave. But he resisted press interviews in the early days. Most colleagues describe Silbermann with the same mix of words: thoughtful, modest, shy. "Almost frustratingly humble," said Sahil Lavignia, an early Pinterest employee.

Silbermann's press aversion, combined with the service's appeal outside Silicon Valley, limited early media coverage of Pinterest despite its rapid growth. In early 2012, ComScore declared Pinterest had hit the 10 million monthly user milestone in the US faster than any independent website ever.

"It never had its media moment," said Lipsman, who was previously SVP of marketing and insights at Comscore. "It was sandwiched between Twitter's hyper-growth, and then almost immediately after came Instagram and Snapchat. Just as Pinterest had its chance to shine, it was competing for attention with other key players."

One former employee said they felt Snapchat's success was the most "heartbreaking" to watch. It launched after Pinterest and "took away all the new shiny object" fascination with the latter. Even now, with Pinterest set to have its moment on Wall Street, the employee noted how difficult it is for brands to "get cool again."

The Pinterest playbook: Move slow and debate things

In 2016, the year Snapchat's parent company began prepping for an IPO and Instagram rocketed to 500 million monthly users under Facebook's ownership, the Pinterest team had a drawn out back-and-forth over the word "save."

True to its name, the company offered a "Pin it" button to encourage users to add items to their Pinterest boards. Tests showed changing it to the more intuitive "save" label would boost user engagement, especially outside the US, but some questioned whether it would be at odds with the Pinterest brand. "Save" won out, but only after a debate that one former employee said "took a long time to get through."

The process was emblematic of the pros and cons of a company taking a more thoughtful approach to building up its audience and revenue. Under Silbermann's leadership, Pinterest was careful not to rush to make changes simply to juice growth. He pushed for "more research and discussion before jumping into a particular strategy," Ansari said. In the process, he built a distinct brand, but frustrated some employees by, they say, taking too long.

Scott Belsky, an early Pinterest investor, said Silbermann explained his thinking by referencing his experience growing up in a family of doctors, in which you are expected to study for years before ever getting a chance to operate. "He always thought about applying what he was exposed to in the world of medicine," Belsky said. "Getting something right regardless of how much time it takes, as opposed to constantly moving fast and breaking things."

Each year, Silbermann would "proclaim a theme" for the team to focus on, Belsky said. One year might be monetization, the next might be going international. "It was his way of pacing the company ... and getting all [the] energy to get something right," Belsky said.

But Pinterest didn't always get its pacing right. The team initially underestimated just how much they'd need to invest to build an advertising product that could compete with the sophisticated standards set by Facebook and Google, according to two former employees. "They just didn't have enough engineers working on the product," one former employee said.

This may have made Pinterest's road to going public even longer.

"A bully in the market"

Pinterest lists several competitors in its IPO prospectus, ranging from predictable names like Facebook and Snapchat to shopping services like Amazon and lifestyle verticals like Allrecipes. But its most dangerous competitor may be the service Pinterest mentioned parenthetically alongside Facebook: Instagram.

Both services launched in 2010. Both focused on visual content and satisfy our appetite for foodporn and home decor ideas. But unlike Pinterest, Instagram was inherently viral. It tapped into existing friend networks, attracted celebrities and influencers, and benefited from Facebook's backing.

"They were always two months ahead of us on the growth curve," said Weiner, the early Pinterest employee. Another former employee said Pinterest's team viewed Instagram as the "biggest threat."

With Facebook's backing, Instagram topped 1 billion monthly active users in 2018, dwarfing Pinterest. It is increasingly stepping on Pinterest's toes — not unlike it did in the months before and after Snapchat's parent company went public.

Last month, Instagram made it easier to shop within the app, two weeks after Pinterest added more shopping features. Instagram is also said to be testing public "Collections," similar to Pinterest's core feature. Instagram rolled out the option to save posts in private collections in 2017.

"The biggest competitor to Pinterest isn't Amazon. It's Instagram," said Kathleen Smith, principal at Renaissance Capital, which manages IPO-focused exchange-traded funds. "All Instagram has to do is add like features. They are kind of a bully in the market."

Even with that threat, some insiders still believe Pinterest can be a service used by everyone. "I think we have to admit it's a little slower getting there," said Probasco. "But I think the mission is massive: the idea that we can connect everybody to the things they love and help them discover new things they love. It's a human need."