I was one kilometre away from the finish line of a marathon I had no business running. It had been an absolute, hamstring-straining slog. Five hours of physical and psychological punishment. But it was almost over, I'd almost completed my mission impossible and as I rounded the corner of Macquarie Street for the final downhill sprint to the Opera House, I was buoyed by the sight of my run club friends (who'd finished more than an hour ago) waving and cheering me on.