The idea is that everybody else dies with certainty, from your observation point, but you yourself can't, because the denominator of the probability fraction consists only of those futures where you exist.
It happens to be a vivid idea to me, because a long time ago I read a short story that was more fantasy/horror than science fiction, but resembled it a little in spirit. It was about a kid in a small town who discovered that the grave digger for the town seemed to know ahead of time who would die, and dug the graves in advance. The kid thought this was just mildly interesting as long as it was just elderly people he didn't care about, until one day his parents were in a car accident and because one grave was ready, he knew one was going to die. He killed the grave digger and buried him in the open grave instead, and from then on, people stopped dying. Which turned out to not be a blessing.
It happens to be a vivid idea to me, because a long time ago I read a short story that was more fantasy/horror than science fiction, but resembled it a little in spirit. It was about a kid in a small town who discovered that the grave digger for the town seemed to know ahead of time who would die, and dug the graves in advance. The kid thought this was just mildly interesting as long as it was just elderly people he didn't care about, until one day his parents were in a car accident and because one grave was ready, he knew one was going to die. He killed the grave digger and buried him in the open grave instead, and from then on, people stopped dying. Which turned out to not be a blessing.