I got a phone call from a friend yesterday that took me straight back to August 08. A friend of a friend, one whom I liked quite a bit but never really got to know, died suddenly while he was home alone. He had two high school age daughters; one of them found him when she got home from school.
While I don't think there really is an answer for "why" this happens, beyond the obvious medical explanations, I still think it's terribly unfair that some people get more time than others. I think it's especially sad when good parents don't get as much time as they should with their children, and children lose their parents early in life.
All I can think is that we have to remember that we don't know when our time will be up, so make the most of every moment. Spend time where it matters - close to those you love.