The Hawthorne Effect is a behavioral bias where people change what they do because they know they are being observed. In cyber security, that matters because measurement can alter the very workflow you are trying to study. Users may follow policy more closely during a pilot, ticket handlers may close cases faster when dashboards are visible, and analysts may behave differently when they know logs, reviews, or audits are being watched.
This effect can distort both defense and attack analysis. A new control may look successful during testing but lose effectiveness once attention fades, or an attacker may become quieter when monitoring is obvious. That is why defenders prefer passive telemetry, repeated baselines, and long-running metrics that survive beyond launch day. The goal is to measure real behavior, not just behavior shaped by being observed.