He explains that imposter syndrome is a psychological phenomenon in which people - often facing a new or big challenge - are unable to internalise their accomplishments, attributing their success instead to luck, timing or some other external factor beyond their own making.
"Despite a continual striving for excellence that usually results in success, these individuals believe that they have tricked others into thinking they are bright and that it is only a matter of time before someone "outs" them as frauds.
"Imposters experience terror when they think of failing at some goal that they set for themselves, and they take drastic measures not to make a mistake or lose the respect of others."
A surprising number of people in the workplace have imposter syndrome. Hillman explains the symptoms: "An imposter is self-absorbed, more serious than fun, careful and cautious, constantly scanning for incoming threats, unlikely to acknowledge a shortcoming or mistake, unwilling to yield to a better idea, and unable to relax and be 'in the moment'."
He says if a person is in any degree of "stretch" related to a new role, or broadening their current role, or has been assigned to fix a huge problem, there's a tendency to experience self-doubt and to begin questioning whether they have the capability to succeed.
"When this happens, the person is inclined to withdraw inwardly in an attempt to mask those feelings. At the very time they should be reaching out to learn from others, they're inclined to pull away.
"This is when an individual is likely to be in the firm grasp of imposter syndrome."
He says that when the symptoms are at full throttle, the fear and panic begin to rise, perpetuating a direct connection between what the person is thinking and how they are feeling.
"A person with imposter syndrome becomes a person in mental freefall, spiralling with a dreadful sense that they are about to make a fool of themselves.
"When this happens, you are inclined to deflect attention and focus away from yourself. Imposters are masters of deflection."
Hillman says he was inspired to write his book because: "I find the syndrome to be one that is commonly faced by so many, but there's a general reluctance to talk about it openly out of fear that no one else can relate.
"I hope the book generates good dialogue and debate about how authentic leadership can and does make a difference, both to individuals and to organisations. I want to 'normalise' the syndrome as a first step in stripping it of its adverse potency."
Hillman suggests that the way to get away from imposter syndrome is through being authentic.
Someone who exemplifies this, Hillman says, is Sir John Kirwan.
"I have come to admire legendary All Black Sir John Kirwan," he said. "He suffers from chronic depression, and for a good deal of his early adult life and professional career he chose to suffer in silence, afraid that his teammates and fans would consider him weak, or worse, if he chose to make his illness public.
"But Kirwan decided to come forward and talk openly about depression and the damage it can do to individuals, families and communities. And by doing so he has set an example for many others and paved a way, particularly for boys and men, to acknowledge the devastating impact of an illness that can be treated, and in many cases cured.
"By making himself human, Kirwan's leadership has brought to light a purpose and a cause that thousands are willing to support him on. It's an example of how getting others to follow your lead is most directly tied to being real about who you are."
So what exactly is this authentic leadership that Kirwan exemplifies?
Hillman says: "Whether you are a CEO or a team leader or a newly appointed intern, your best weapon of influence is your own authenticity.
"The more connections you are able to make with another person, the more likely you will be able to relate to each other and potentially move forward on something you both consider important," he says.
"It is no different with a team or a group of people. You create bonds through those things you have in common.
"To find the things you have in common with others, you have to be willing to give of yourself.
"And to give of yourself simply means you are willing to let others see you are human. That includes all those things that fall short of perfection."
Many people, particularly leaders, fear being seen as vulnerable. Yet part of being an authentic leader means allowing yourself to be exactly that.
Hillman says: "Vulnerability is very much like breathing - so long as you're alive, they both just happen naturally.
"You can overthink breathing, just like you can overthink vulnerability. It's part of life ... nothing more, nothing less."
Val Leveson is an Auckland-based counsellor.
