We identify a friend-number paradox, that is, a mismatch between people’s preferences for the friends they might acquire in social interactions and their predictions of others’ preferences. People predict that others are attracted to them if they have a relatively large number of friends. However, they personally prefer to make friends with someone who has a relatively small number of friends. People regard a large number of friends as a signal of social capital that increases their interpersonal attractiveness. However, it can actually be a signal of social liabilities that diminish their ability to reciprocate obligations to others. We conducted a series of studies, including three speed-friending studies in which participants either engaged or expected to engage in actual interactions for the purpose of initiating long-term friendships. These studies provide converging evidence of the hypothesized mismatch and our conceptualization of its determinants.