My first experience of loss occurred when my grandmother passed away. I was sitting at home watching a documentary on UFO's when my mother suddenly received a call. As she was speaking into the phone, I could see the tears well up in her eyes and as she kept the phone down she could not help but break down completely. Seeing her in tears, I started crying too not knowing what was going on or why my mother was crying. I was 10 years old then. Today, about 14 and a half years after my mother is smilingly preparing breakfast in the next room. What changed? Why is my mother not crying now? Because the mourning is over.
"Time is the greatest healer" is one of the oft repeated statements when dealing with loss. People always get better the greater the time between today and the sorrowful event. So, if people do EVENTUALLY get better, why then is there an initial sadness? What is the purpose of mourning?
Many songs, books and travelogues have been written documenting the mourning process. My favourite is Neil Peart's Ghost Rider: Travels on the Healing Road and the legendary Into The Wild. Both of these document a significant psychological trauma after which the protagonist travel 'away' from the source of the trauma to heal their wounds respectively.
Mourning as a phenomenon is not merely a social custom in man but can be seen in mammals such as elephants, dogs and other primates as well. Therefore it ought to provide an evolutionary mechanism for something - I believe it to be a motivation of creating distance from the traumatic event. Notice that death in the animal kingdom is very rarely self inflicted as in man, but more due to the presence of a predator or some other environmental agent. Therefore if a certain member of the species were to die, the process of mourning might prevent other members of the group form venturing into the same area thereby avoiding the cause of death of the member. It could be the same mechanism that makes time a great healer of trauma since receiving more positive feedback from the environment, over the course of time (even if the environment is the same eg. the same house where the traumatic event occurred) would create the same impression of 'moving away' from the source of the damage.