The Only Thing Keeping You Unhappy is the Belief You Are Alone

This is what Don's "ex"-wife tells him in the penultimate episode of Mad Men. I love thinking through these sort of statements. What sense of "alone" is meant? Is she saying the Don is alone because he fails to see that he has people in his life that love him? Is he alone because he doesn't allow for the possibility of mystery--of something unexpected and unpredictable to happen that can improve one's life?

Surely there are moments when all of us feel "alone." They hit me when the person or people I am closest too cannot seem to grasp what I am feeling or when I cannot find words to express what I think. Some people feel alone when they contemplate death--the idea that in the end you are on your own in that moment.

But, for people to feel alone, while they are surrounded and loved by others seems almost like an illness, and yet it is all too common.

What I am wondering about is what is the opposite of believing you are alone?