Narcissism in personality trait generally conceived of as excessive self-love. In Greek mythology, Narcissus was a man who fell in love with his reflection in a pool of water. Thus, The NPI was developed by Raskin and Hall (1979) for the measurement of narcissism as a personality trait in social psychological research. Hence, It is based on the definition of narcissistic personality disorder found in the DSM-III. But, it is not a diagnostic tool for NPD and instead measures subclinical or normal expressions of narcissism. So, even someone who gets the highest possible score on the NPI does not necessarily have NPD.