GoPro founder Nick Woodman sold his first camera in 2004. The enthusiastic surfer had been frustrated by the inability to get up-close photos of his surfing, so he assembled a rugged and simple camera that could be strapped to a wrist. As he improved the cameras and ways to mount them, they caught on with the surf community, then skiers, bikers and more.

By the 2010s, point-of-view videos from GoPro users caught fire on YouTube and Vimeo, generating hundreds of millions of views. The amazing videos became free viral ads for the cameras. Extreme sports enthusiast had to buy one. The company’s single greatest coup came when Felix Baumgartner, who strapped on a GoPro for his jump from space in 2012. Those videos alone have been watched tens of millions of times.

When GoPro was first coming to market, it seemed as if Nikon, Sony and Canon were bankrupt. As video cameras in smartphones got better, the need for a stand-alone device eroded. With the digital camera space under siege, rather than innovate, the incumbent players were frozen in the smartphone headlights. It took a startup to re-imagine the video camera and ignite new growth.

GoPro employed a smart marketing strategy. Rather than positioning its products as rugged camcorders, they chose to evangelize a whole new type of device. By proclaiming the value of a wearable sports camera, GoPro avoided the declining camcorder market. In consumers’ minds, GoPro had no competition. Like Twitter (TWTR), Facebook (FB) or Google (GOOG), GoPro marketed its technology as a different, new idea, unlike anything else on the market. And it worked.

By May of this year, when GoPro released its S1(the document companies file describing their business to investors) for its public offering, the company could say it controlled 70% of the wearable sports camera market. That’s brilliant — because before GoPro, there was no such thing as a “wearable sports camera market.”

This is what a legendary startup does: It creates a new market and installs itself as the market’s king. By defining a new space competitors have to play by the new king’s rules — to their disadvantage. The king winds up with a huge market share and its competitors get squat. Today it would be almost impossible for Canon or Nikon to keep up with GoPro.

This brings us to the IPO. When going public, a company needs to say where it’s going, not just where it’s been. Investors need to believe a gigantic new opportunity awaits. When done well, a public offering does more than raise money. IPOs can be market-defining events. That makes an S1 the perfect chance for management to explicitly define for the public the market the company is creating and all of the explosive, multi-dimensional ways that market will grow. In other words, instead of just discussing the company, define the category.

GoPro’s S1 does some of that. It expands GoPro’s vision from making cameras to building an ecosystem that will include video editing and sharing services and a plan to “scale as a media brand.” Instead of just making an immersive sports camera, GoPro wants to be seen as an immersive sports company.

We think GoPro could have pushed this harder and used the S1 to describe an immersive sports category and how it will explode worldwide in years to come. We’d like to hear what that category will look like and how it will change our lives — and how GoPro will lead it and dominate it like a benevolent dictator. And then we’ll know: If GoPro can build a legendary category, it will certainly flourish as a legendary company.

Al Ramadan, Christopher Lochhead and Dave Peterson are co-founding partners at Play Bigger Advisors (www.playbigger.com), a San Francisco-based firm that coaches technology executives to build market-leading companies. Follow @playbiggeradv