Sean Ellis on Testing Product-Market Fit Across 600,000 Books and 16 Countries

Why a Million Books Doesn't Mean a Million Growth Teams

When Sean Ellis learned his Chinese publisher had sold 600,000 copies of Hacking Growth, he did the math. Sixteen languages worldwide meant he and Morgan Brown were closing in on a million total sales. But the vanity metric hid a harder truth.

"You've got almost a million books sold. You've got these great education programs like GoPractice, like Reforge. And so there's a lot of knowledge out there, yet the number of companies are actually executing growth in a really effective cross-functional way is tiny," Ellis said.

That gap triggered a 100-day world tour across 16 countries. The goal wasn't more book sales. It was to find the missing link between reading about growth and actually doing it.

The Workshop Format as a Before-and-After Moment

Ellis has been refining his growth workshop since 2017, when Microsoft bought 5,000 copies of his book and then called him. The head of growth for Office 365 said the team was "really having trouble implementing it" and thought a workshop could help.

What makes the format work isn't the teaching. It's the forced collaboration. Ellis spends 30% of the time giving instructions on a 9-part framework. The other 70% is cross-functional teams—product, marketing, engineering, data—making decisions together in real time.

If you don't have everyone on the same page around why experimentation is important, what you're trying to accomplish, and then all the way back up to how do customers actually get value from this product, what is the system that creates really happy customers? You end up wasting so many cycles debating.

— Sean Ellis

The workshop creates a pivot point. Before it, teams argue about whether to experiment. After it, they've already decided how many experiments to run per sprint, who owns what, and where the biggest opportunities are. Ellis charges $40,000 for a private session. On the world tour, he ran them with 10 companies at once, each at their own table, making it accessible at scale.

The "Ellis Test" Became the SES at Nubank

Ellis didn't expect to hear his product-market fit survey called the "SES" when he visited Nubank in Brazil. The neobank grew from 40 million to 90 million customers in roughly two years—almost entirely through organic growth, not paid marketing.

The head of product, a former Facebook exec based in Silicon Valley, finally asked his Brazil-based team: "What the heck is this SES you guys are always talking about?" It was the Sean Ellis Survey. The company had embedded the PMF question into their culture from the early days.

That survey alone was super powerful in helping them not just understand that they have product market fit, but really deeply understand that product market fit so that they could leverage that in how they built sustainable growth in the business.

— Sean Ellis

Ellis also met the team that built TikTok's growth function at ByteDance. They told him their playbook came from his blogging—before the book even existed. "That's definitely the company with the biggest reach that I've had a direct impact on," he said.

In Japan, one of the country's rare repeat unicorn founders sat down for lunch and said the same thing: "The Ellis test really helped us in both companies."

It's Not Just a Metric—It's a Lens

The original insight was simple: if 40% of users say they'd be "very disappointed" if your product disappeared, you have product-market fit. Below that, don't scale. Above it, build your growth engine.

But the real power comes from pairing the question with follow-ups. What features make this a must-have experience? What outcomes matter most? That's when it shifts from a threshold test to a tool for deepening fit over time. Ask it to every new audience cohort. Track how answers evolve. Strengthening PMF becomes a competitive advantage.

Entrepreneurship and Growth Hacking Share the Same DNA

Ellis found a tight correlation between a country's appetite for entrepreneurship and its readiness for growth hacking. Both require the same thing: willingness to fail.

Japan has low entrepreneurial risk tolerance. Ellis felt it immediately. "Countries where there is a really high level of entrepreneurship tend to do better with growth hacking than countries that don't," he said.

Indonesia surprised him. Strong entrepreneurship, scrappy founders. Australia punches above its weight for its population. Latin America has "super passionate people with a high tolerance for risk" and startups to match.

If you're not cranking out startups, I can't change the culture of a country. That's a really hard thing to do. For me, that was one of the fun things about this trip around the world—to find these pockets of entrepreneurship.

— Sean Ellis

India puzzled him. Massive IT talent, strong services companies, but surprisingly few world-stage product companies beyond Zoho. He told The Economic Times that India has "underperformed their potential"—not the most diplomatic take, but one he believes will challenge the right people.

China, on the other hand, flipped the script. Once known for cheap plastic gadgets, it's now a technology powerhouse. Ellis credits part of his book's success there to the translator—a former LinkedIn data lead who ran Growing.io in China. Domain expertise in translation isn't vanity. It's distribution.

Speed Beats Perfection When You're Learning

Ellis launched the world tour with about four months of prep. He was still negotiating partnerships at the end of the trip while delivering workshops at the start. He reached out to LinkedIn connections in each city and asked: "Who are the thought leaders in growth here?" Two or three names always rose to the top.

He picked partners off reputation alone. Some were big agencies. Some were solo advisors. No exact formula. Most of them were great. One still owes him money.

"If I had spent 2 years planning, you know, same way if you're launching a product, you can spend all this time sort of in the boardroom. My velocity of learning was so much higher the way that I did it," Ellis said.

He referenced Guy Kawasaki's Rules for Revolutionaries: "Don't Worry, Be Crappy." Sometimes you just have to get out there and do it. The learning comes from motion, not planning. Ellis now knows exactly what kind of partner works best, which approaches drive ticket sales, and where to invest his energy next time. He won't do another world tour. But he'll do regional ones—and he'll be smarter.