The statistic I check every morning is not the one on my dashboard

I created an awesome dashboard. MRR, signups, DAU, churn, one chart each. I stared at it religiously for months, but it never once gave me a clue as to what to do next.

What I do look at now is a Slack channel, that tells me whenever somebody takes their first action within the product, along with when they signed up. If the interval becomes bigger than ten minutes, I know something's broken in our onboarding. It has spotted two bugs before users reported them.

This dashboard is for the investors. This channel is for me.

What is your own? I am collecting examples of such single metrics that turn out to be way more valuable than full-fledged analytics system for their owners. I'll share the list with you.