One of my best friends for the past 35 years is rapidly deteriorating.

Each time I visit, I’m stepping into a difficult new reality. I enter his house. I climb the stairs. And then there he is. Sitting in his space-age mobile chair, in the center of his sunlight-filled living room. His head is tilted and he’s doing his best to smile at me.

The disease that took hold of him has destroyed his body. He can’t talk. Any movement is difficult. And yet his mind is still fully intact. He’s still in there–...