To succeed socially, you must make people feel included. But there's a catch: people most want to be included by those they see as EXCLUSIVE.
One of the best feelings in the world is to feel like you are included in an exclusive group.
Humans by nature want to join groups. More specifically, they want to join valuable groups, that they benefit by being members of. One of the primary ways humans determine the value of a group is by how exclusive it is.
Just think of that old Groucho Marx quote:
"I refuse to join any club that would have me."
It's funny, because the humor is self-deprecating ("any club that finds me acceptable as a member can't be a club worth joining"). But it also highlights a subtle truth: the value of the club hinges on how exclusive it is.
Nobody feels good about his inclusion in a broadly inclusive group. People want to be included into exclusive things.
This simple truth has a great deal of weight for your social and romantic interactions, too... because excellence with other people often comes down to how included you make them feel, in your own personal exclusive club.