I don't understand.

Today a co-worker of mine lost his 16 month old baby boy to brain cancer. I had only met this little boy a couple of times, but I am more shaken up than I ever thought I would be. He was only diagnosed 4 weeks ago, and today he is gone. In 4 weeks he went from running around and laughing, to lying in a hospital bed, taking his last breaths in his parents' arms.