During the formation of friendships, people reciprocate favors and support quickly to avoid the impression of exploiting the other person (Lydon, Jamieson, & Holmes, 1997). In established friendships, however, such tit-for-tat behavior (immediate reciprocation; Axelrod & Hamilton, 1981) is detrimental as people value balanced relationships,

Interactive motifs are a person’s typical cognitive, affective, and behavioral propensities to think, feel, and act in certain ways across situations. Applied to relationships, interactive motifs reflect how individuals think about other people, respond to them emotionally, and engage with them.

Friends typically are defined as people who mutually select each other for friendship; with whom one shares companionship, interests, and values; in whom one can confide; and for whom one feels concern and affection. Friends are expected to be trustworthy with respect to giving solid advice and holding confidences, to engage in appropriate levels o

Individuals develop strategies to make contacts, to start friendships, and to maintain but also to end voluntarily these relationships. Behavioral motifs vary by gender, social status, life stage, family status, and other personal characteristics. They are highly influenced by personality traits that moderate openness to new contacts

“there is nothing intrinsically natural about separating all human beings into two opposing categories on the basis of one physical attribute of their overall being-in-the-world” (Rawlins, 2009, p. 125

Similarity in traits, attitudes, or interests among friends may be a byproduct of social homogamy (e.g., meeting in the neighborhood where people of similar socioeconomic status and political orientation live; McPherson et al., 2001) and further environmental factors influencing friendship formations (e.g., meeting during shared leisure activities

Children are more positively engaged with friends than nonfriends, with more smiling, talking, sharing, cooperating, and helping, and they show more effective task performance with friends. Although children are just as apt to engage in conflict with friends as with nonfriends, conflict resolution differs: Friends are more likely to use negotiation

More extraverted people dress more stylishly, behave more confidently, and express more positivity, for instance through smiling—factors that make extraverted people attractive to others and make others like them better (Back et al., 2011

People differ in their networks and maintain either (1) relatively few long-term, emotionally close friends, (2) larger networks with close friends and also loose acquaintances, or (3) even social networks without friends and only family ties.