Both as a psychological and a legal concept closely linked to loss experiences. Surviving family members may believe that the loss of their loved one was unjust, whether that loss caused by intended violence, fate, disease, etc. Leads to derogation of victims. People Must Grieve to Move Beyond Major Loss C. Wortman's evidence that parents of children dying of SIDS had not grieved significantly in 18 months and yet were in good psychological health. Lots of concerns about such data.
Some cultures believe in rapid psychological movement beyond grief.
See Margaret Stroebe et al.