Our first paying customer had not used the product once

We found out about six weeks in. Not churned, not unhappy, not complaining. Had simply never logged in and sent a single thing.

The uncomfortable part was that nothing in our own dashboard told us. We were watching signups and revenue. Both looked healthy. Usage was the number that actually mattered and it was the one nobody had put on a screen.

Two things I took from it.

A signed customer who has not used the thing is not a customer. It is a refund with a delay on it.

Revenue is a lagging indicator of a decision someone already made weeks ago. Usage is the leading one, and it is the only number that tells you anything useful on a Tuesday.

We went back, rebuilt the onboarding live with them on a call, and it did work out. But we lost a month purely because we were measuring the comfortable thing instead of the true one.

Curious what the equivalent was for other people here. What was the metric you were not looking at, and what did it cost you to find out?