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.
For a long time our empty state was a box that said: drop a document here.
Reasonable. It's a tool for reading long documents, so of course it needs a document. But watch what that actually asks of a first-time visitor. Go and find a file. Make sure it's the right one. Make sure it's long enough to be worth the trouble. Upload it. Wait. Only then do you find out whether the thing is any good.