9/11 - The psychology of remembrance

This September marks the 11th year since our lives were indelibly changed on a sunny Tuesday morning. Although it has been over a decade, we still remember that day like it was yesterday. We tend memorialize tragic events, disasters, death and loss. Why do we actively try to remember tragic events, disasters, and significant loss? What is the role of memorials, anniversaries and days of remembrance in our process of healing?