Mourning, by Saul Bellow, in a letter to Karl Shapiro:
"...losing a parent is something like driving through a plate-glass window. You didn't know it was there until it shattered, and then for years to come you're picking up the pieces--down to the last glassy splinter."
This beautifully nails the way grief reappears unprovoked. All that's missing from it is that you're actually picking the glassy splinters out of yourself : splinters you thought you were finally done extracting, until something unaccustomed reminded you.