A couple of theories that I have.
My theory is that you can never imagine the unimaginable. I can see you, shaking your head. can't imagine the unimaginable. Silly girl, everyone knows that. But, really, stop and think for a moment. An example; Craig Scott. His sister was killed in the Columbine shooting. Now, imagine what you would do in his situation. Having to go, day to day, know that that happened. You can't do it, can you? Can't imagine how you would keep on going. Every day, feeling that hole where your sister was. My theory is that we can't imagine the unimaginable, big things, people we love dying, unless it happens. Our bodies and minds jerk us back, not allowing us to go to deep into that sensation, because it might overwhelm us, and we'd we thrown in too deep. Or maybe it's just me.