Object permanence is the first lie we learn. Peek-a-boo. Mommy's
  still here even if you don't see her. The ball is still here
  even when it rolls around a corner. There's no need to cry. Then
  you lose a favorite toy. Then somebody is gone for too long.
  Then somebody dies. We get sent right back to the days before we
  learned the first lie, and remember the first truth: We don't
  know what happens to things when we don't see them anymore. We
  can't predict if we'll ever see them again and that is very very
  hard to bear because are anticipation machines... and the one
  thing we can never anticipate for certain.... is anything. The
  best we can do is hope.