How much of what we call 'reality' is actually out there or rather within our own head?

What constitutes the authentic human being?

Grief causes you to leave yourself. You step outside your narrow little pelt. And you can’t feel grief unless you’ve had love before it - grief is the final outcome of love, because it’s love lost. […] It’s the cycle of love completed: to love, to lose, to feel grief, to leave, and then to love again. Grief is the awareness that you will have to be alone, and there is nothing beyond that because being alone is the ultimate final destiny of each individual living creature. That’s what death is, the great loneliness.

Insanity - to have to construct a picture of one's life, by making inquiries of others.

You know what the doctor said to me to cheer me up?" Fat said. "There are worse diseases than cancer." "Did he show you slides?" We both laughed. When you are nearly crazy with grief, you laugh at what you can.

Why is love so good...? You love someone and they leave. They come home one day and you say "What's happening?" and they say, "I got a better offer someplace else," and there they go, out of your life forever, and after that until you're dead you're carrying around this huge hunk of love with no one to give it to. And if you do find someone to give it to, the same thing happens all over.

The distinction between sanity and insanity is narrower than a razor’s edge, sharper than a hound’s tooth, more agile than a mule deer. It is more elusive than the merest phantom. Perhaps it does not even exist; perhaps it is a phantom.