Why does a person feel lonely even when they are surrounded by hundreds of people?

Feeling lonely is synonymous with the feeling of depression and mostly an outcome of the imbalance in social harmony. It is the lack of intimacy or the level of it with a person or a community that you desire or deserve. It's a privilege only for humans to feel lonely and no other living creatures possess this unique feature of feeling bored or lonely. Fulfillment of the social circle quantitatively or qualitatively may also be one of the reasons