Like Narcissus who, according to the Greek myth, fell in love with his own reflection, sufferers from narcissistic personality disorder develop an unhealthy sense of grandiosity, becoming obsessed with a fantasy of their own success, power and capacity for love.
But people with the disorder may be extremely sensitive to criticism, or to any kind of defeat. When confronted by a failure to fulfil their high opinion of themselves they can easily become enraged or severely depressed.
Barry George, the killer of British TV presenter Jill Dando, was a serial fantasist and sufferer from the disorder. He posed as an SAS soldier, pretended to be a professional stuntman and insisted he was the cousin of Freddie Mercury, lead singer of The Queen.
John Hinckley, who shot US President Ronald Regan in 1981, was found not guilty of attempted murder on the grounds of insanity after he was diagnosed with the disorder.
Everyone has personality traits - characteristic ways in which they respond to stress. But although people tend to respond to difficult situations in the same way, most will adopt a different approach if their first response is ineffective.
In contrast people with personality disorders are so rigid they can't adapt to reality, are unaware their pattern of behaviour is inappropriate and often believe it is normal and right.
Of almost a dozen types of personality disorder, the narcissistic disorder is marked by a pattern of self-centred or egotistical behaviour that persists despite causing problems at work or in relationships with other people.
It normally begins in adolescence or early adulthood and is difficult to treat. As sufferers believe they are superior to others they expect to be admired and often suspect that others envy them.
They feel they are entitled to have their needs attended to without waiting, so they exploit others whose needs are deemed to be less important. Some are only mildly affected but in more severe cases the condition may lead to missing days at work or school, alienating family and friends and a risk of suicide or criminal behaviour.
In the worst cases, sufferers may become totally isolated, lose touch with reality and withdraw from social contact and be at high risk of harming themselves or others.
David Holmes, a psychiatrist at Manchester Metropolitan University, said: "Someone who has narcissistic personality disorder is very selfish, has a sense of entitlement, in that they expect praise and things to be given to them, and to be treated almost as royalty, most of the time, by most people."
People with the condition first manifest it by talking about themselves, their work and their lives as if there is no one else in the picture.
They give the impression they are bearing heroic responsibility for their family or work because others are unreliable, unco-operative or otherwise unfit. They ignore and denigrate the contributions of others and complain that they receive no help at all.
Their stoicism may win admiration but they lack sympathy and empathy and they will use other people to get what they want without caring about the cost. Their behaviour is usually seen as offensive, self centred and arrogant.
- INDEPENDENTBy Jeremy Laurance