When Simon Yates cut the rope and sent his friend plummeting to an ordeal few mountaineers can have contemplated, the outcome was totally unpredictable.
That Joe Simpson survived is a revelation of the power of the human spirit to overcome fear, pain and deprivation of almost unimaginable intensity.
He did not expect to live it all over again - more than once.
The first test was to write his award-winning account of the ordeal in Touching the Void.
That meant dragging the terrifying experience out of the deeper shadows of his memory.
Then, another fall in the Himalayas crippled and almost broke him.
Yet he felt forced to test his nerve again and struggled on crutches to 20,000 feet on Pumori, near Everest.
On his descent he heard that a young first-time climber had been killed by a chance rockfall.
What sense could he make now of this game of ghosts that had claimed the lives of so many of his friends.
This extraordinary memoir is Joe Simpson's attempt to find catharsis and some explanation for the urge he felt since childhood to measure fear and embrace the unknown.