I'd say it would be impossible to fully know about every human on earth even if there were like 10,000 people total. The human brain has a certain capacity for maintaining relations, and once you cross the size of a small community/village it's basically all the same.
Are you really any more isolated from 8 billion people than you were from 7 billion?
Are you really any more isolated from 8 billion people than you were from 7 billion?