As Heidegger says what we have to realize is that our own death is a reality and everything else pales before that reality, which we are last to focus on. He talks about how dasein becomes authentic by facing its own demise, and with that the loss of its world, and by extension the loss of everything in ones world. Dealing with losses of others, or of things is of less concern in most cases when one is alone facing ones own death. But as I have said the ultimate in loss is the loss of ones children because one would rather die oneself than to have them die. So beyond what Heidegger says there is something greater, deeper, more profound which is the loss of a child of ones own. That is why genuineness, and sincerity is deeper than authenticity. There are losses deeper than the loss of oneself, or even ones spouse. And this very fact that the loss of the other from oneself is deeper than the loss of oneself, or one’s partner and spouse is enough to give us hope. Because ultimate loss is outside ourselves.
The hard truth is that you do not move on from that, It is an open wound always with you, that you never overcome. You do not deal with that. You do not handle it. It is the greatest weight in existence and you have to bear it, and bearing it makes us human in the highest degree. This is because we know we will die and we place our hope in our children. But when the children die before we do then some part of that hope is crushed and there is nothing that can replace it, even if you have other children who live. But of course the worst is if you have only one child and it dies or all your children die as often happens in war. The suffering of mothers that have lost all their children is unthinkable. But it happens and the mothers live, but never recover. And the fathers too suffer deeply. It is our capacity for suffering that makes us human.
The fact that we are guaranteed the pursuit of happiness does not mean we actually obtain it, except perhaps briefly, fleetingly, and then everything is gone, but worse than everything and everyone we know being gone is if our children are suddenly gone either though illness, or accident, or violence and war. We live with that suffering, and it never leaves our consciousness, and we are all the more human for it, because we could love that much that we would place another’s life before ourselves if we had the chance.
Nietzsche showed us how to make our suffering the path to our humanity.