MAU is lying to you What numbers do you look at to find the truth?

Tracking logged in users made our numbers look great on paper but when we checked actual usage people were just clicking around and leaving.

Logins don't mean much if no one is getting value.

We started tracking how many users complete one core action every week instead. It was a slap in the face at first but it saved our product.

For anyone building a SaaS what is the single metric that tells you people actually care about your tool?