This is an expression used by William Gibson in a short story he wrote called "Hinterlands". The protagonists of Hinterlands are sort of exobiological psychiatrist-whores: they greet and aid (with all their being) to help a returning star-traveller reattach to the rest of humanity. They haven't had a single success yet; all the travellers wind up insane or dead. The protagonists, those closest to the returners, can feel why- plain human sympathy shares the image across the borders of madness, of disconnection on a scale no one can come back from:
"Now it was vast, the very hollow of night, an emptiness cold and implacable. It was last words, deep space, every long goodbye in the history of our specis. It made me cringe, whining. I was shaking, groveling, crying. ... It's the Fear. It's the long finger of Big Night, the darkness that feeds the muttering damned to the gentle white maw of Wards. Olga knew it first, Saint Olga. She tried to hide us from it, clawing at her radio gear, bloodying her hands to destroy her ship's broadcast capacity, praying Earth would lose her, let her die..."
I find this turn of phrase very interesting, for one reason: it fits the mindset of every disturbed person I know. The touches of madness; the suicidal impulses in my group aren't the simplistic, thumbnail "I can't deal with the grief" escapes so many people envision. I have stood too close to the impulse that a person has found a remorse so great, so deep, that they can never share it with anyone -- and that the bearer is afraid of inflicting on anyone. It is a mindset of egoism, grief, and selflessness that I find terribly, terribly sad, and a tiny bit seductive.