I think death emotionally brings us back to a very early time in
  our lives, before we had words and had only uncertain emotional
  responses and a world and body and mind that just didn't make
  sense;

  One of the first lessons we learn is permanence of objects.
  Peek-a-boo. "Guess what? your ball is still here!" "Guess what?
  Mommy's still here."

  One day, there's death in your life and you're aware that
  peekaboo was a lie. One of your first learning experiences shot
  to hell and all you can do is go back to the emotional state of
  your first loss, the no-words sensation - the existential crisis
  of object impermanence - and the initial trust gained that was
  then broken.