Ostracism is the deliberate social exclusion of an individual or group. Being ignored, excluded, or rejected by others activates a powerful and often painful psychological response.

Laboratory studies show that even brief, minimal forms of exclusion—such as being left out of a simple ball-tossing game—produce reports of distress, reduced self-esteem, and a lowered sense of belonging and control. Brain-imaging research indicates that the experience recruits some of the same neural regions involved in physical pain. Prolonged or repeated ostracism is linked to depression, aggression, and withdrawal.

Humans are highly sensitive to cues of inclusion and exclusion because belonging has been critical to survival. The pain of ostracism can motivate efforts to reconnect, yet it can also lead to defensive or antisocial reactions when reconnection seems impossible. Social media and workplace environments create new contexts in which ostracism can occur subtly and persistently.

Being left out hurts. That hurt is the psychological signature of ostracism.