Dramatic title right? well, it's a pretty dramatic topic. When you choose to not monitor the digital experience, you're sort of slamming the door on your user's face...you're being selfish!
DEM stands for Digital Experience Monitoring or, if you're paying attention, Management. It's the idea of understanding your user experience and how it's perceived by your users. Your site could be running beautifully on a few EC2 instances using almost no CPU or memory but, if the users can't get to what they're looking for, that efficiency is undercut by a bad user experience. That's when you get all sorts of post on forums and social media saying, "Your website is terrible" or, "You need a new IT team".
You can talk to those disgruntled users and try to get screenshots, a customer ID, steps to reproduce (and you probably should) but, this isn't going to help you long term. You probably figured out APM (Application Performance Monitoring) a while back and can at least detect if a server goes down...lets tackle the experience.
Am I Using DEM?
This is DEM.