There's one thing that my Human Resource Management lecturer always used to say -
Each person is unique. People can be differentiated with their skills, abilities, ideas, intuitions or such qualities. But being unique doesn't mean that we wanna stay away from each others. People mostly working together to be effective and efficient instead of being individuals to achieve goals. They always find something similar among them to get connected and stay in touch. Something they all love. Like you and me. Yeah,
Common Interests. People love to get together and
talk and share about them. That is where the need of a "Group" pops in. Don't you wanna get into a group and share interests with like-minded people rather than exposing all of them to public or other friends who are not interested in?