In the sequence of the emotional development of the individual, friendships come after parental bonding and before the pair bonding engaged in at the approach of maturity. In the intervening period between the end of early childhood and the onset of full adulthood, friendships are often the most important relationships in the emotional life of the adolescent, and are often more intense than relationships later in life. However making friends seems to trouble lots of people; having no friends can be emotionally damaging in some cases. Friendships play a key role in suicidal thoughts of girls.
A study by researchers from Purdue University found that post-secondary-education friendships (e.g. college, university) last longer than the friendships before it.
Children with Autistic spectrum disorders such as Asperger’s Syndrome and autism usually have some difficulty forming friendships. This is due to the autistic nature of some of their symptoms, which include but are not limited to preferring routine actions to change, obsessive interests and rituals, and usually lacking good social skills. This does not mean that they are not able to form friendships, however. With time, moderation, and proper instruction, they are able to form friendships after realizing their own strengths and weaknesses. Children with ADHD may not have difficulty forming friendships, but they may have a hard time keeping friendships because of impulsive behavior and hyperactivity. Children with inattentive ADD may not have as much trouble keeping and maintaining friendships, but inattentiveness may make it more difficulty.

Ancient Greece

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A topic of moral philosophy much discussed by Plato, Aristotle, and the Stoics, but less so in the modern era, until the re-emergence of contextualist and feminist approaches to ethics. In friendship an ‘openness’ of each to the other is found that can be seen as an enlargement of the self. Aristotle writes that ‘the excellent person is related to his friend in the same way as he is related to himself, since a friend is another self; and therefore, just as his own being is choiceworthy for him, the friend’s being is choice-worthy for him in the same or a similar way.’ Friendship therefore opens the door to an escape from egoism or belief that the rational course of action is always to pursue one’s own self-interest, although escaping through the door would require finding what is covered by Aristotle’s ‘same or similar way’. It is notable that friendship requires sentiments to which Kant denies moral importance. It is a purely personal matter, requiring virtue, yet which runs counter to the universalistic requirement of impartial treatment of all, for a friend is someone who is treated differently from others. One problem is to reconcile these apparently conflicting requirements