Doctors have suggested that health care professionals should use criteria in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) to diagnose similar mental disorders properly. It is important not to confuse various mental illnesses as some symptoms are pretty much similar.
As for the set of symptoms that point to the narcissistic personality disorder, health care providers mention the following: stressing your achievements and excellent performance; desiring to be treated as a superior one; being obsessed by the idea of self-significance; wanting others to admire you all the time; requiring constant attention; living in imaginary world where your life is perfect (better than others have); being unable to evaluate personal strengths and weaknesses soberly; overestimating personal role in many things; taking advantage of people around to make personal wishes come true; behaving aggressively or annoying concerning others; staying envious and jealous when other people are lucky, even if those are close people; having no respect for the feelings of people around.
Some people might say that it is okay to be confident and ignore weaknesses, but it’s a bit different. This condition does not look healthy at all. Besides, believing in own superiority in all fields may end up dramatically if the person does something risky trying to stress its significance.