Managing one EC2 is easy. SSH in, run commands, done. That one becomes ten, becomes hundreds, becomes thousands, everything collapses. How to distribute keys and rotate them, who did what when for audit, should port 22 be internet-exposed, how to safely apply patches simultaneously across thousands. AWS Systems Manager (SSM) exists to address "fleet-scale operations" directly. One name, actually ten independent features: Run Command, Session Manager, Patch Manager, State Manager, Inventory, Automation, under one umbrella.