The best product metrics measure more than activity. They capture whether users are actually finding value. But what happens when teams start optimizing the number instead of the experience?
Airbnb: Nights Booked
Airbnb chose nights booked because it directly reflects its core value: connecting travelers with places to stay. Unlike app downloads or website visits, bookings represent actual transactions.
How to game it: A team could push aggressive discounts or encourage longer stays to inflate bookings. Nights booked might increase while profitability, guest satisfaction, and booking quality decline.
Facebook: 7 Friends in 10 Days
Facebook’s early growth team popularized this metric after observing that users who connected with friends early were more likely to stick around. Seven friends served as a proxy for reaching the point where Facebook became socially valuable.
How to game it: Teams could aggressively recommend random connections or pressure users to add people they barely know. Friend counts would rise, but meaningful social connections might not.
Slack: 2,000 Messages
Slack found that 93% of teams that exchanged 2,000 messages continued using the product. This threshold suggested that Slack had become part of a team’s daily workflow.
How to game it: Teams could encourage unnecessary messages, splitting conversations into multiple posts or generating more notifications. Message volume would increase while productivity decreased.
The Takeaway
These examples illustrate Goodhart’s Law: when a measure becomes a target, it can stop being a good measure. Each metric originally captured something valuable: successful stays, meaningful connections, or productive communication. But optimizing it blindly risks destroying the very value it was designed to represent. The lesson is that metrics should guide product decisions, not replace judgment.
