• Before the 20thcentury, about 5% of all households (about 1% of the world population) consisted of just one person. That figure began rising around 1910, driven by urbanization, the decline of live-in servants, a declining birth rate, and the replacement of the traditional, multigenerationa...

It is an umbrella term we use to cover for all sorts of things most people would rather not name and have no idea how to fix.
Plenty of people like to be alone. But solitude and seclusion are different from loneliness. Loneliness is a state of profound distress.

We crave intimacy. And yet, long before the present pandemic, with its forced isolation and social distancing, humans had begun building their own separate cells. 

Before modern times, very few human beings lived alone.

Our bodies perceive being alone (or with strangers) as an emergency. Thus, our nervous system evolved to produce the anxiety we associate with loneliness.
We breathe fast, our heart races, our blood pressure rises, we don’t sleep. We act fearful, defensive, and self-involved, all of which ...

... is that lonely people can’t see that lots of people feel the same way they do.
Loneliness seems to be such a painful, frightening experience that people will do anything to avoid it. We shut down the lonely, afraid that this might be some kind of a contagious situation.