A great many introverts, especially early in life, believe that they are the only one.

They yearn for some sense of belonging in a society that seems to reject them at every turn.

Later in life, there is no way one can explain what it was like. That it was not just one of the normal pains of growing up. That it was to see all of society in motion as if entombed behind a pane of thick and impenetrable glass.
One grows up with a completely different background from everyone else, can never really confide or ask for understanding. Isolation begets isolation. Every year one grows farther still from the sunlit world. In time one gladly travels down the divergent path enjoying the fulfillment the other way promises to all yet delivers to far too few.

At the beginning of the moonlit path
When one is young and outcast,
There is a lonely sort of torture
To be the only one
Is a very different thing than being alone