One of the things they didn't tell you about adulthood is that it's hard to make friends.

Take it from The New York Times, who report that as you get older:

"it becomes tougher to meet the three conditions that sociologists since the 1950s have considered crucial to making close friends: proximity; repeated, unplanned interactions; and a setting that encourages people to let their guard down and confide in each other ... This is why so many people meet their lifelong friends in college."

So once you're out of college — and, say, moved to a new city — those conditions are harder to meet.

Take New York for example: You have to be super dedicated to schlep to see your buddy on the Upper West Side if you're coming from Brooklyn. Outside of the workplace (which has its own host of friendship retardants), those repeated, unplanned interactions are hard to come by. Then there's the mutual exchange of confidences, which requires increasingly scarce levels of privacy.

This is problematic, since friends are so important to our lives.

Let's count a few ways:

• You get jobs come from friends.

• Your happiness comes from friends.

• Your weight (or weight loss) is related to your friends.

• You quit smoking with your friends.

• You get ideas from your friends.

• You'll live longer if you have close friends.

• Your romantic partnerships will be better if you have close friends because you'll be able to spread your complaints between people.

So how can we grown-ups make friends? Let's take a few pointers from New York Mag's Science of Us blog and sprinkle in a few further insights.

To begin, we need to note the "mere exposure effect," a psychological theory that states people tend to like things that they're familiar with. The more you eat Thai food, the logic goes, the more you'll develop a taste for pad Thai. The principle carries over to social psychology: the more time people spend with you, the more they'll acquire a taste for you, or so the research suggests. For example, you'll feel greater fondness for someone who works in your building than a total stranger.

Second, there's the matter of getting into situations where you have repeated interactions. Here, Reddit users have some suggestions, like frequenting a uniquely awesome bar, going regularly to a friendly gym, volunteering at the animal shelter, or joining any flavor of club.

Relatedly, people feel closer to one another after they've confided something. Psychologists call it "self disclosure"; in the research, it predicts liking, closeness, and relationship building. So when you're getting lunch with your colleagues, don't just talk about the weather or the sorrow you feel from the United States losing in the World Cup. Actually say something about your personal history and the projects you're arranging your life around.

Most satisfyingly, you can deepen your friendships by asking people for stuff.

"Friends make us happy if they make us feel like we matter," explained "Friendfluence" author Carlin Flora. "They make us feel needed. That means if you never ask your friends for favors, they don’t get that satisfaction of feeling needed by you."

So, if you need a ride to the airport, you know who to ask.