A desire to belong is deeply rooted in people. Our ancestors depended on group cohesion to survive. The latest research with barbary macaques shows that other mammals can also suffer from social isolation. The negative feeling of loneliness can be understood as an important warning signal: Social pain drives us to cultivate contacts with other people. But that can be a difficult undertaking in a world in which digitalization and individualism are increasing and family ties are gradually dissolving. Various initiatives are opposing this trend. They aim to understand what loneliness does to us and to help those who are unable to overcome a lack of relationships on their own. Politicians are also dealing with the issue: The United Kingdom recently created a minister for loneliness. The filmmakers visit lonely people in Hamburg, Berlin, Switzerland and the British town of Frome and talk to psychologist Maike Luhmann and friendship researcher Janosch Schobin about the latest scientific findings on the causes of loneliness.