People are so attached to their phones that they're missing out on a resource successful people have used for centuries

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Sit with your own thoughts and feelings.

• Spending time alone - without your phone or computer - is linked to greater creativity, productivity, and happiness.
• According to Cal Newport, author of "Digital Minimalism," we all need to do it more often.
• Newport personally takes long walks when he's working on tough problems or wants to self-reflect.

The "loneliness epidemic" is upon us.

A 2018 survey by health-insurance company Cigna found that most Americans, especially millennials and Generation Z, are considered lonely.

And yet, in his new book, "Digital Minimalism," Cal Newport makes the case for solitude, and argues that we're not getting nearly enough of it.

Newport is a Georgetown University professor of computer science and the author of the 2016 bestseller "Deep Work." In "Digital Minimalism," he guides readers in reducing the amount of time and energy they devote to digital technology, in an effort to help them focus on the people and activities they really value.

So when Newport talks about solitude, he's talking specifically about the tech-free kind. Think a solo walk in nature (sans phone) or a few minutes spent in quiet contemplation (sans computer). Unfortunately, he writes, we're currently experiencing a cultural phenomenon he calls "solitude deprivation," or "a state in which you spend close to zero time alone with your own thoughts and free from input from other minds."

The problem? Newport writes: "When you avoid solitude, you miss out on the positive things it brings you: the ability to clarify hard problems, to regulate your emotions, to build moral courage, and to strengthen relationships."

Newport cites a few different expert sources suggesting that spending an excessive amount of time on your phone can lead to anxiety and depression. Even if you don't take this leap of logic alongside him, it seems plausible that browsing social media and responding to a flurry of texts might leave us in an existential void, stuck somewhere between enjoying the company of others and enjoying our own.

Spending time alone may be difficult at first, but it's important

A potential solution, then, is to put the phone down every so often and either socialize in person or be truly alone. Newport spends more time on the second option, noting that, like many successful people before him, he often takes long (solo) walks, to work through a problem or engage in some self-reflection.

A growing body of research lends Newport's argument credence. For example, letting your mind wander (which you could, technically, do in the presence of another person) can facilitate creative thinking.

Read more: A productivity expert says this 15-minute daily exercise can make you more successful

Psychologist Scott Barry Kaufman found that many people get their best ideas in the shower. "The relaxing, solitary, and non-judgmental shower environment may afford creative thinking by allowing the mind to wander freely, and causing people to be more open to their inner stream of consciousness and daydreams," Kaufman has said.

The main difference between loneliness and the kind of solitude that makes you more successful is that the latter is voluntary. As Kenneth Rubin, a developmental psychologist at the University of Maryland, told The Atlantic, one of the requirements for productive solitude is that you can join a social group when you so choose.

Newport, for his part, readily acknowledges that it can be hard to make time for solitude in your daily schedule. What's more, it can be uncomfortable to sit with your own thoughts and feelings without the escape button that is the Facebook app icon.

Matthew Bowker, a psychoanalytic political theorist at Medaille College, told The Atlantic, "It might take a little bit of work before it turns into a pleasant experience. But once it does it becomes maybe the most important relationship anybody ever has, the relationship you have with yourself."