Here is an excerpt from an article written by Michael Maccoby for Harvard Business Review and the HBR Blog Network. To read the complete article, check out the wealth of free resources, obtain subscription information, and receive HBR email alerts, please click here.

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Donald Trump is an official phenomenon. The real estate tycoon and TV celebrity’s ongoing success as a presidential candidate shows that he has clearly struck a chord with many voters. It has also confounded many citizens and pundits who predicted that Trump’s arrogant putdowns and grandiose claims would doom him to quick rejection by Republican voters. How is it that after outbursts that would not be tolerated in a schoolroom, Trump’s relationship with his followers just grows stronger? What do his followers like about Trump?

The answer may have as much to do with Trump’s achievements as his proposed policies. Unlike his rivals, he has made a fortune by his own efforts; he can convincingly claim he is his own man while his rivals are puppets, indebted to the big money donors his followers distrust.

But his appeal may have even more to do with his personality. No one pushes Trump around, and no insult goes unanswered. He fights back. He is not cautious or fearful of offending a critic or any of America’s adversaries. In this, Trump has a personality type that’s common to the charismatic leaders who emerge in times of turmoil and uncertainty, when people are ready to follow a strong leader who promises to lead them to greatness. Sigmund Freud called people with this personality type “normal narcissists” and he described them as independent and not vulnerable to intimidation, also noting that they have a large amount of aggressive energy and a bias for action. Freud included himself in this group and saw these narcissists as driven to lead and to change the world. Such narcissists can be very charming, and indeed, research has shown most of us like to follow narcissists.

I have done much additional study of leaders such as these, whom I call productive narcissists. The results of this research were first published in my Harvard Business Review article of 2000, “Narcissistic Leaders: The Incredible Pros, the Inevitable Cons” (which was later expanded into a book). I wrote that productive narcissists like Steve Jobs, Bill Gates, and Larry Ellison were exploiting new technologies to create great companies, just as Andrew Carnegie, John D. Rockefeller, and Henry Ford did over a century ago. However, I also illustrated that people with this personality type, however brilliant, have potential weaknesses that can do them in.

They can become so tied to their visions that they lose touch with reality. They can become so self-important and thin-skinned that they lash out at subordinates who question them. They can act as though the rules don’t apply to them. They can end up isolated in their own worlds.

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Michael Maccoby is a globally recognized expert on leadership who has advised, taught, and studied leaders of companies, unions, governments, healthcare organizations, and universities in 36 countries. He is President of The Maccoby Group and author, most recently, of Strategic Intelligence: Conceptual Tools for Leading Change.