Many of the world's great leaders are narcissists. Self-belief, ambition and energy drive their pioneering creative spirits and often this has a positive effect on business. Why is narcissism such a dirty word, then? Because its flipside can be collateral damage as it impacts on staff, and promotes risky, illegal or immoral behaviour and greed. An egotistical leader may suffer as well, as he or she loses a sense of self. Psychologists say the root cause of the disorder is found in childhood. Coincidentally, even Sigmund Freud, the father of psychoanalysis, was a case in point. How can the advantages of narcissism be harnessed and the destructive consequences avoided?