Your perception of reality shifts to match others.

In 1935, Sherif found that people converge on a shared estimate when viewing a stationary dot of light in a dark room.

The light appears to move due to the autokinetic effect, a visual illusion caused by involuntary eye tremors. When participants make judgments alone, they create a personal standard; when in groups, they immediately adopt a social norm. This shows how quickly individual perception dissolves into group consensus.