Muscle memory is the habit of performing repeated actions automatically, with little conscious review. In cyber security, that can be helpful when users and administrators practice safe routines, such as locking screens, verifying URLs, or following a standard login procedure. It makes work faster and reduces friction in busy environments.
The downside is that attackers often try to exploit automation in human behavior. When a person is moving on autopilot, they may click a phishing link, approve a fake MFA prompt, enter credentials into a spoofed page, or accept a dialog without checking details. Security training often aims to replace risky habits with secure ones, because the moment a task feels routine is often the moment attention drops.