It's what your mother always told you: to make a friend, you have to act like one. Research on the transition from acquaintanceship to friendship shows that people getting to know each other adopt what psychologists call a "communal script," responding to each others' needs instead of demanding tit for tat. But because they risk embarrassment if the other person doesn't share their desire to get closer, they protect themselves by paying careful attention to all that their potential pal says and does. "When people are in transitional relationships, each interaction carries more weight, has more consequence," says John Lydon, Ph.D., of McGill University in Montreal.
Participants in Lydon's study of "preunit" relationships, as he calls them, said that they would be just as likely to accept a request for a favor from a potential friend as from an established one, but that they would feel less comfortable carrying it out. When they imagined that the potential friend had done them a good turn—say, paid for dinner—subjects thought the gesture had more meaning, and were more anxious to return the favor, than if it had come from an old friend.