The phenomon most people have fewer friends than their friends have, on average. This was first observed by sociologist Scott L. Feld in 1991.
It is a form of sampling bias, as any given person is more likely to be friends with people who themselves have lots of friends. This also applies to other social graphs, such as number of sexual partners.
Hilariously, most people believe they have more friends than their friends have.
On the bright side, the people you are not friends with have fewer friends than you do.