Mourning is an essential aspect of psychological and spiritual growth in individuals and of political growth within organizations and nations. A good mourning, including elements of reminiscence, sadness, and anger, readies us to go on with an openness to new possibilities. Mourning also requires us to examine and come to terms with our own relationship with the lost object or experience. Failure to mourn, on the other hand, evokes defenses like denial, demands for restoration of that which never fully was, or submission to a nostalgia that maintains attachment to the lost and now idealized object. Here, I delineate between healthy and foreclosed mourning. The role of nostalgia as an entry into mourning or a defense against it is discussed. The consequences of failure to mourn losses are exemplified in a former patient, the Roman Catholic Church, and in the United States post-9/11.