Tellingly, chained or tied up and left behind to die is a recurring trope in human myths and stories, from the Prometheus myth to maidens left out for dragons to the Crucifixion itself. It shows up again and again in modern movies and TV; even in Westerns, characters get buried up to their necks in sand and left to die.
It is a major human fear. We know it’s bad when it happens to us. We’ve got no excuse for doing it to anyone else, let alone our “best friends.”