Case · M2-M3 × Start (social network)
Facebook: 7 friends in 10 days
Facebook's growth team compared users who stayed with users who left and found a setup milestone: reaching 7 friends within 10 days. Onboarding was then aimed at connecting new users fast. The number comes from a public talk; its derivation was never published.
The outcome · 2016
“7 friends in 10 days” as Facebook's activation milestone, per growth leader Chamath Palihapitiya's public talk and repeated by Index Ventures (Nov 28, 2016). Correlational; the exact derivation was never published. Reforge frames it as a setup threshold whose aha moment is an interesting feed.
CorrelationalPress-reported
Read the sourceStage cell: M2-M3 × Start (social network).
What they did. Compared engaged and churned cohorts, named the milestone that separated them, and pointed onboarding (friend suggestions, contact import) at reaching it within the first days.
The mechanism. Habit Path mining HK-MEA04 (Hooked Ch.8) and steering people to the habit-predictive action rather than the easiest one HK-ACT21 (Hooked Ch.3). Curating a follow graph is the user's first investment HK-INV14 (Hooked Ch.5): it makes the next visit's feed worth opening.
The outcome. 7 friends in 10 days (2016) Case grade C. Press or secondary reporting. as the stated activation milestone; correlational.
What it means at your stage. At M2, look for a setup threshold (connections, data imported, teammates invited) that precedes the aha moment, and measure how fast new users reach it. Validate it with a test before treating it as causal F26.
Caveats. A first-party talk known through secondhand retellings (number grade C); no published method. Mechanism link Evidence grade B. Moderate evidence: solid studies with some limits., correlational.
Would you have called it?
This case is also a round of Predict the Outcome: read the situation, pick what you think happened, then see the evidence.
Play this roundTry this
The techniques behind it
Each one is a starting point, not a recipe. Gamify It turns a technique into an experiment card for your product: the change, the metric, the guardrail and how long the test needs at your traffic.
- TechniqueEvidence grade C. Limited evidence: few or small studies.
Steer new users down the Habit Path
make the action that predicts retention the easy path
Find the early action that predicts who stays, confirm it with a test, then make it the easiest thing to do in onboarding. The easiest action is not always the habit-forming one: on one network, searching was the likeliest first step, but following accounts built the habit.
- TechniqueEvidence grade D. Practitioner framework or anecdote: plausible, untested.Practitioner heuristic
Codify: count habitual users and map the path they share
habitual-user rate and Habit Path
Set a realistic cadence for a devoted user, count the share of each signup cohort who meet it, and compare what those users did in their first days with users who left. The book's rule of thumb: below about 5% habitual, you have the wrong audience or a product to rethink.
Limits
What we don’t claim
- The Hook Model is a practical design tool, not a validated or complete theory of behavior.Hooked, Introduction
- The evidence is correlational until it is tested in your product.
- The threshold is a heuristic, not a measured cut-off.
- No success is attributed to a single technique: real outcomes have many causes.
- Company names are used editorially; no endorsement is implied.
Sources
Hooked · Nir Eyal
Ch.8 · Ch.3 · Ch.5
Growing as fast as Slack · Index Ventures, 2016
Case grade C. Press or secondary reporting.Define user activation moments · Reforge
Case grade C. Press or secondary reporting.
Source IDs: HK-MEA04HK-ACT21HK-INV14F26
Book content is paraphrased, never quoted at length. Last verified October 24, 2026.
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