Sean Ellis's 40% fit survey and North Star Metric, run in a small company

Who Sean Ellis is and what he proposes

Sean Ellis is co-founder of GrowthHackers.com and, according to his publisher's author page, coined the term "growth hacker" in 2010. With Morgan Brown he wrote Hacking Growth (April 2017), which presents growth as a disciplined, data-driven process run by cross-functional teams that test continuously across the whole customer lifecycle: acquiring, retaining, engaging and monetising customers.

Two of his ideas have travelled furthest: a one-question test for product/market fit, and the North Star Metric.

The "very disappointed" product/market fit survey

The core question is short:

"How would you feel if you could no longer use this product?" — Sean Ellis

Respondents choose between "very disappointed", "somewhat disappointed" and "not disappointed" (some versions add "not applicable"). As described in First Round Review's account of Superhuman, Ellis benchmarked nearly a hundred startups and found that those struggling to grow almost always had fewer than 40% "very disappointed" responses, while those with strong traction almost always exceeded it. In a 2024 Lenny's Podcast conversation, the recommended next step is to study the "very disappointed" group and use what you learn to sharpen positioning, messaging and features until that group reaches 40%.

The best-known application is Superhuman's. The email company scored 22% at first. By segmenting to the personas most represented among "very disappointed" users, and later by spending roughly half its roadmap doubling down on what those users loved and half on what held back "somewhat disappointed" users who valued the same main benefit, it reported reaching 58% within three quarters. Superhuman's survey added three follow-up questions: who would benefit most, what main benefit they receive, and how the product could be improved.

The North Star Metric

The second tool aligns the team once you know what customers value.

"The North Star Metric is really trying to quantify that value over time." — Sean Ellis, Intercom podcast

In that 2018 Intercom conversation he gave Airbnb's nights booked and Facebook's daily active users as examples. The 2024 Lenny's Podcast write-up lists criteria for a good one: it reflects the core value customers receive, it is actionable and not a ratio, it can grow over time, it correlates with revenue without being revenue, and its direction is clear to the whole team.

The same conversation sets out an investment order for growth work: activation and onboarding first, then engagement, referral and the revenue model, and acquisition last. Ellis has long stressed onboarding; in the Intercom interview he recalls that at LogMeIn, retention improved markedly when users had a great first experience.

Why it matters for a small company

SMEs rarely lack ideas; they lack focus. The survey tells you whether the proposition is strong enough to scale and, more usefully, for whom. The North Star turns that answer into a number that marketing, sales, operations and product can all influence. Together they stop a small team spreading effort across campaigns that grow the wrong customer base.

Playbook: run both in six weeks

1. Choose who to survey (week 1). Survey people who have genuinely used your product or service recently, not your whole mailing list. Opinions from people who never experienced the value will skew the result.
2. Send four questions (weeks 1–2). Use Ellis's question plus the three Superhuman follow-ups. For a B2B firm, ask by email from a named person; for e-commerce, after a delivered order.
3. Read the result honestly (week 3). Treat 40% as a benchmark, not a pass mark. A small sample can swing easily, so look at who answered as well as the percentage.
4. Profile the "very disappointed" group (week 3). Which segment, use case and main benefit dominate? This is your best-fit customer and your core value proposition.
5. Rewrite the proposition (week 4). Update website headline, sales deck and onboarding to speak to that group's main benefit, in their words.
6. Pick a North Star (week 5). Ask: what action shows a best-fit customer getting the core value? Examples by business type: repeat orders per month for a food retailer; active projects delivered on schedule for a service firm; qualified enquiries for a lead-generation site, provided they reflect customer value rather than vanity.
7. Map the inputs (week 5). List the three or four drivers your teams can move (activation rate, repeat frequency, referral rate) and assign owners.
8. Review weekly, re-survey twice a year (week 6 onwards). Track the North Star weekly; repeat the survey to see whether changes reach the people who matter.

Limits and criticism

• The 40% line is a heuristic. In a 2019 critique, Justin Jackson notes that Ellis has called the threshold somewhat arbitrary and argues that asking people to predict future feelings is unreliable. He suggests pairing it with past-behaviour questions and hard metrics such as retention.
• Mature products. Jackson also argues the survey is most useful early on; established products with habitual or locked-in users may score differently from how customers actually behave.
• Revenue as North Star. Choosing revenue looks sensible but hides whether customers are getting value. Ellis's criteria deliberately keep revenue as a consequence, not the target.
• Metric theatre. A North Star nobody can influence becomes a slide, not a steering tool. Keep the input metrics owned.

FAQ

Sources

• Hacking Growth (book page) — Sean Ellis and Morgan Brown / Penguin Random House, 2017
• Hacking Growth (UK edition and author bios) — Penguin Books UK, 2017
• The original growth hacker reveals his secrets — Lenny Rachitsky with Sean Ellis / Lenny's Podcast, 2024
• Sean Ellis on charting a path toward sustainable growth — Intercom, 2018
• How Superhuman Built an Engine to Find Product/Market Fit — First Round Review
• Is the Product-Market Fit survey accurate? — Justin Jackson, 2019