Grief, at times, does allow us to enjoy the memory of a moment gone by or the feeling of a dream of the deceased one. Somewhere in that, however, we realize that feeling won't last forever.
When I have described my grief I always say
"It's like being the sickest one has ever been and going to the medicine cabinet or to the doctor and knowing nothing can make the pain go away."
As one begins to heal and learn to cope with (or become numb to) the pain, it is also realized that this moment of pain won't last forever.
In grief, in joy, in hurt, even in times of indifference moments don't last forever.
It is up to us to adjust and learn to embrace or endure the moments we are given.