If you are a consumer PM, you likely spend a lot of time analyzing patterns of user behaviour on your product. If it’s a web product, you likely spend a decent percentage of this time in Google Analytics. You may also have specialized analytics systems, but GA is often a PM’s go-to for quick ad-hoc analysis.
Over time, you will use this ad-hoc analysis to build mental models about your product and your users. The problem arises when you treat these behaviours as static. Over time, the same data points you use to build your understanding of user behaviour can become a liability. Eventually they will go stale and then rancid, like a forgotten cup of yogurt in the back of your fridge.
Intelligence Alerts in GA is an under-utilized tool that can help you with this. You can use it to codify your assumptions about user behaviour, and get alerted if they change. Set notification thresholds calibrated to your perceived lower bound on normal usage behaviour. When a niche but important feature breaks silently a few months from now, you will be the first to know.