Feeling connected to others is a basic need. It is present from birth and continues throughout life, and people are social by nature. Everyone feels lonely at some point; loneliness is the feeling of being separate or distant from others when you want to feel close, connected, or part of something. Having lots of social connection does not mean a person never feels lonely. It does reduce lonely feelings and helps people get over them more quickly. Adults who have strong social connections have a lower risk of many health problems. Older adults with close friends are likely to live longer than peers with fewer friends; being friendly to others, even people you do not know well, is one way to build social connection.

Researchers at the University of Kansas estimated how long a friendship takes. It takes roughly 50 hours together to move from acquaintance to casual friend, 90 hours to become a friend, and more than 200 hours to become a close friend. The hours do not all count equally. In that study, time spent hanging out and joking around counted toward friendship, but hours spent working together did not count as much; friendship is shaped by how we spend time, not only how much. Time at work or school, where people have to be anyway, and shared-interest activities did not clearly make participants feel closer. Making a friend takes time together, and you cannot make one in an instant; friendship takes time together, so try to see new friends often and check in with them in between.

In the same Kansas research, more time talking did not by itself make friends feel closer. Students grew closer through catching up on their lives, playful talk, serious conversations and showing affection. Pure small talk tended to leave them more distant; friendship was also an investment. Students who turned an acquaintance into a friend about doubled their time with that person and spent about half as much time with other friends, whose friendships did not grow. A researcher named Hall suggests students may make friends faster than adults because of something about student life, such as the close quarters of college living. It could also be that students overestimate how deep their friendships are. How good your friendships are counts more than how many friends you have.

Hall based his work on earlier studies suggesting that a person's brain can handle only about 150 friendships. Many adults find it hard to make new friends because work or caring for family can come first, or because of moving or growing apart. Researchers named a liking gap: people systematically underestimate how much their conversation partners like them and enjoy their company. After you talk with someone new, the other person usually likes you and enjoys your company more than you think they do; researchers Boothby, Cooney, Clark and Sandstrom tested the liking gap in a series of five studies. Some of them used pairs of strangers who had a 5-minute conversation with icebreaker questions and then rated how much they liked each other and how much they thought their partner liked them.

One explanation for the liking gap is that people are self-protectively pessimistic. They do not want to assume the other likes them before they find out if that is really true. Another is that people seem too wrapped up in their own worries about what they should say to see the signals of liking that outside observers see right away. In a study of real college roommates, the liking gap lasted for several months rather than disappearing quickly; the liking gap may keep people from pursuing relationships with others who truly do like them. Sometimes the trouble is the setting, not the person. In a place where few people share your interests, it can be hard to find your group.

In the 36-question closeness exercise, partners take turns answering and asking. They spend about equal time talking and listening. Pairs who took turns answering each question liked each other more and felt closer than pairs where one person spoke at a time; the exercise works partly because both people open up at the same time and at a similar pace, so sharing does not feel one-sided. It mirrors the gradual getting-to-know-you process that relationships usually go through. A good conversation also goes back and forth; share something about yourself rather than only asking questions, and give the other person a turn to talk. Sharing about yourself, and your feelings, helps friends feel close to you. Being a good listener means asking what is going on in a friend's life and letting them know you hear them.

Researchers at Dartmouth found they could predict who were friends just by looking at brain responses to video clips. Friends had the most similar neural activity patterns, then friends-of-friends, then people three steps removed; the Harvard Study of Adult Development began in 1938 with 724 participants: 268 Harvard College sophomores and 456 young adults from Boston. In that study, people who were most satisfied with their relationships at age 50 were the healthiest at age 80. The Harvard study found that close relationships were better predictors of long and happy lives than social class, IQ or even genes; the benefits of relationships can come from anywhere: family, friends, work colleagues, and even small pleasant chats with the person who makes coffee or the cashier at the grocery store.

Toddlers watch each other and play side by side first. Later children play together, share ideas and build on each other's play; children can form simple friendships starting in the second year of life. They begin as a preference for one person and later become reciprocal, give-and-take relationships. Language and communication skills are powerful building blocks of friendship, and as preschoolers' language grows, their play with peers becomes more elaborate; in one study, mothers' calm, sympathetic talk with children about bad moods was linked to stronger self-regulation later. Stronger self-regulation was linked to better peer relationships as children got older. Successful friendship depends on skills such as handling introductions and conversation, cooperating and compromising, and apologizing and making amends.

When adults ask children to think of other explanations for a hurtful action, such as an accident or a bad day, children are more likely to give the other person the benefit of the doubt. Children as young as 4 are more likely to forgive a peer for wrongdoing if that peer actively apologizes. Apologizing is not enough on its own, though; in an experiment with 6- and 7-year-olds, children felt better only when the person who knocked down their tower helped rebuild it. Knowing how to solve a disagreement peacefully matters for friendship, and adults can teach steps such as naming the problem and cooling off. Learning to form successful friendships is a critical skill for kids, and one they keep using and refining all their lives.

Researchers who study the Harvard group say it is never too late. Many people who thought they were no good at relationships found them at a time they did not expect. They call keeping up a social life social fitness; like physical fitness, it is a practice, and tiny actions such as sending a text to someone you miss count. Making friends is not a magic trick. It is something people learn, and it gets easier with practice. Friendships take effort to keep going, and without it, friends can drift apart. A parent, teacher or other trusted grown-up can help you decide whether someone might make a good friend; parents and teachers can help a child who finds it hard to make friends. A grown-up you trust can help.

Words to know

• loneliness: feeling cut off
• pessimistic: expecting the worst
• reciprocal: give-and-take
• participants: study volunteers