The Privacy Paradox (psychologytoday.com)

You may not be physically alone throughout the day, but you're probably not interacting in a meaningful way with the people around you. Even the people we see regularly often remain strangers, and the bigger the city, the more likely you are not to know the woman who delivers your mail or the man at the counter of your local coffee shop. We pass our days in the company of existential strangers. The net effect is one of malaise—dysthymia—because we are toiling, eating, and sleeping amid people who remain distant and aloof.

As evolutionary psychologists point out, humans developed in tight tribes. People were aloof only when they were actively rejecting one another. Hence the ping of irritation or concern we feel when an e-mail goes unanswered, a phone call ignored. Hence, too, the oppressive feeling we can get from being constantly surrounded by strangers—even if we can't articulate the source of our discomfort.

For most of human history solitude occurred only in small doses; wander off on the savannah and you'd be dead. Today, all you have to do is lock the door and turn off your phone.

We arrive at the 21st century as profoundly social beings who risk severing their own lifeline. With the exception of parent-child and romantic relations, we no longer hug, kiss, and hold each other for warmth, protection, and reassurance. Our interactions have become vastly more sanitized. No one's complaining about central heating, but our spectrum of communication is severely restricted. Today it's inappropriate to brush up against someone you like or even to look them in the eye too bracingly.

Modern life allows us to become too self-absorbed, immersed in hurt, self-protection, and sadness.

What to do? Nurture your connections with people you like and people who may require your help. You can be selective, but one thing that we know about combating dysthymia is that when you treat others kindly and fairly, refuse to nurture a grudge, and throw yourself into creative endeavors, your mood lifts. Only by doing that which sometimes feels unnatural—being open to new people— will we override our impulse to withdraw.