“When a measure becomes a target, it ceases to be a good measure.”
This is Goodhart's law.
If you have a product and want to start setting up some metrics that mean something this article for you.
Here's an easy and effective metrics system that you can adopt today:
These three metrics should fit in a triangle, counterbalancing each other.
Once you build a product an effective way to keep improving it and working on the right thing is setting up metrics.
Most of the startup founders I know are really clueless about this.