Reassuringly, the top reason that we add people to our social network, is because we know them in real life.
While some Internet interactions are online-only relationships, the most common reason we add friends on Facebook is because we know people in real life.
According to recent research from NM Incite, for 82% of Facebook users, knowing someone offline is reason to add them on the social network. The next most common reason for adding a friend is having many mutual friends, a practice reported by 60% of users. Mashable