Some people actually fall in love. They live with each other faithfully for their entire lives, and take care of each other until one or the other has died. Once one lover leaves, the other is left in pain. The pain is so great, because the love was so real. And nothing restores the lonesome lover, nothing heals them.
When a wise, beloved, old grandfather tells his children and grandchildren that "time does not heal all wounds," the sadness is brutal. He is so sorrowful, and so honest about it. There is nothing to argue, for he has experienced the real world, and will soon make his exit.
So we're left with our future years. As we go on, we will be severed and damaged until there is nothing left of us. We will celebrate weddings and births, and mourn our dead loved ones. There will be both joy and sadness, for a time.
But every hint of pain is a point in the direction of death. Our own death will be painless though. That is, my death will be painless. I might mourn yours.
When I die, all of those who went before me will welcome me home. Those I leave behind will cry, and will be reminded of what's to come.
Healing will not come. Death isn't a joke.