We have a healthy craving for quiet solitude. I know there are a few people who are afraid of being alone, but the rest of us find it soothing and rejuvenating and it doesn't happen nearly as much as we'd like.
Solitude is therapeutic. Spending time in solitude doing what you want at a pace that is natural to you, without any interruptions, without having to take others into consideration, without any external pressures or the need to hurry, is deeply satisfying and personally I classify it as a psychological need.
It is unnatural for human beings to have no time to think. It serves an important function, I think, much in the same way dreaming does. Dreaming may seem to be a waste of time, but when people are prevented from dreaming — allowed to sleep as much as they want but awakened when they start to dream — after a short while, they begin to hallucinate while they're awake. Dreaming is necessary for mental health.
Solitude and time to think is necessary too, I believe. If you prevent yourself from having time to do nothing, by yourself, allowing free time to think naturally, it makes you less calm, less rational, less happy, less sane, than you otherwise would be. Although I have no experiments I can point to that would validate that assertion, I believe it's true, based on what I know.
In solitude, in the absence of interruptions and distractions, the mind naturally drifts to solving problems, trying out solutions, imagining conversations.
In "primitive" societies, where people don't have the pressures and multi-tasking and so many different forms of diversion, mental illness is almost nonexistent.
Of course, too much time alone isn't healthy either. It's like anything else, you need balance. Not enough exercise is unhealthy, but too much exercise can put you in the hospital. But I think most of us are deficient in solitude and need more of it. Finding it and doing it will require some ingenuity on your part. But you can do it.
Adam Khan is the author of Principles For Personal Growth, Slotralogy, Antivirus For Your Mind, and co-author with Klassy Evans of How to Change the Way You Look at Things (in Plain English). Follow his podcast, The Adam Bomb.