The observer’s presence can become part of the event being observed.

Watching is a form of participation. The presence of an observer alters what people do, how carefully, how honestly, and at what pace, so what you record includes your own effect on the scene. There is no neutral vantage point from which to see human behaviour undisturbed.

This matters for anyone who manages, teaches, parents, or reviews. What you see when you are in the room is a different thing from what happens when you are not, and the difference is not deception so much as physics. If you want to know how something really runs, find ways to reduce your footprint, and treat what you personally witness as one sample rather than the truth.