When an individual is a member of different types of groups, it develops a positive feeling of belongingness. As humans beings it is a need for us to have sociability with others, and to feel that we are a part of a group or community helps us to satisfy that social need.
By being members of groups or associations, we are relating to other humans and that give us the feeling of being a part of the social world. Being secluded from the community we live in is negative for our mental and physical health.
