People generally assume that when they consider another person a “friend,” that person also thinks of them as a friend. In other words, friendship is reciprocal. But when we analyzed self-reported relationship surveys from several experiments around the world, we found that while most people assume friendships are two-way, only about half of friendships are indeed reciprocal. These findings indicate a profound inability of people to know who their friends are, perhaps because the possibility of non-reciprocal friendship challenges one’s self-image. We like them, they must like us.
"Research: You Have Fewer Friends Than You Think" is from hbr.org, published on May 12, 2016