People need each other for different reasons. They need them to do smth, to be smb, to care about them, to be cared, to do their job etc.There are people who say that they  need exact person for exact purpose and it of course sounds very selfish and cruel but how far are we from those people? To desire caring or to have a wish of helping people doesn't seem selfish, but again it's a desire of people themselves so technically these people want it and however unselfish it's their wish. Technically these unselfish people do the same that selfish do. They need people to serve as some mean in achieving some point or in providing needful existence. Or it is more right to see this as a human interaction system? At least it sounds  not so selfish and cold.