It’s now recognized as a universal, and even psychologically beneficial, feeling. But that wasn’t always the case. There are many memorable lines in the closing moments of the 1942 film classic Casablanca, but perhaps none cuts to the bittersweet heart of the moment more than Rick’s (Humphrey Bogart) declaration to his former lover Ilsa (Ingrid Bergman) that “we’ll always have Paris.” That reference to the cherished memory of a finished, but not forgotten, romance helps to fortify the resolve of the former lovers who claim they will never really leave each other, but who are getting ready to do precisely that. Such is the wistful beauty, emotional power and sometimes ruthless practicality of nostalgia — that sentimental longing for the past, including people and places long gone, that affects us all to a certain degree and that researchers today are increasingly discovering the psychological benefits to feeling. But that wasn’t always the case. For centuries, nostalgia was considered to be more of a psychological disorder than a mawkish emotion, a debilitating longing that could require medical attention in those suffering under its influence. | 
