Both as president and in business, Donald Trump is often accused of being overconfident and self-serving. And according to his niece Mary Trump's upcoming book, "Too Much and Never Enough," Donald learned that from his dad Fred's obsession with famous 1950s self help author, Norman Vincent Peale.

Peale, a ministerwho "preached self-confidence as a life philosophy," according to Politico, wrote best-selling self-help book "The Power of Positive Thinking" in 1952, which has since been translated into 15 languages and has sold more 7 million copies.

And while Donald Trump was only 6 when the book was released, Mary says Donald's father was immediately drawn to Peale's teachings. So much so that his family joined the author's church, Marble Collegiate, in midtown Manhattan. (Donald was later married to first wife, Ivana, there in 1977.)

"Fred wasn't a reader, but it was impossible not to know about Peale's wildly popular bestseller," Mary writes in "Too Much and Never Enough," which is set to be released on July 14."The title alone was enough for Fred, and he decided to join Marble Collegiate although he and his family rarely attended."

Mary,55, who holds a Ph.D. from Derner Institute of Advanced Psychological Studies and has taught graduate courses in trauma and developmental psychology, writes that Fred was attracted toPeale's "shallow message of self-sufficiency."

"Peale's doctrine proclaimed that you need only self-confidence in order to prosper in the way God wants you to."

For example, Peale wrote in "The Power of Positive Thinking" that "[O]bstacles are simply not permitted to destroy your happiness and well-being. You need be defeated only if you are willing to be."

Mary writes that Peale's view confirmed what Fred Trump has always thought: "He was rich because he deserved to be." (Fred Trump was a real estate developerwhohad anet worth at around $250 million to $300 million at the time of hisdeathin 1999, according to The New York Times.)

Peale's book touts mantras like "Believe in yourself! Have faith in your abilities!"

A worn copy of Norman Vincent Peale's, "The Power of Positive Thinking."

MediaNews Group/Orange County Register via Getty Images

"A sense of inferiority and inadequacy interferes with the attainment of your hopes, but self-confidence leads to self-realization and successful achievement," Peale wrote.

According to Mary's book, Fred viewed self-doubt as a weakness and passed on these attitudes to Donald "in spades."

Donald Trump and his father, Fred Trump, at the opening of Wollman Rink in Manhattan's Central Park in 1987.

Dennis Caruso | New York Daily News | Getty Images

In 2015, then-presidential hopeful Donald Trump told a crowd at the Iowa Family Leadership Summit that he remembered Peale's church sermons.

"You could listen to him all day long. And when you left the church, you were disappointed it was over. He was the greatest guy," Trump said,according to Politico.

Though Peale had a massive following, he also had critics.According to Politico, Peale was known as "God's salesman" and called a con man because "his simple-minded approach shut off genuine thinking or insight."

Neither a spokesperson for the White House or Marble Collegiate responded to CNBC Make It's request for comment. But on Tuesday, White House deputy press secretary Sarah Matthews said in a statement that Mary's book "is clearly in the author's own financial self-interest."

In the book, Mary says she did not write it to "cash in or out of a desire for revenge." Instead, the events over the last three years that Donald Trump has been president "forced" her hand, she says, and she could no longer remain silent.

"By the time this book is published, hundreds of thousands of American lives will have been sacrificed on the altar of Donald's hubris and willful ignorance. If he is afforded a second term, it would be the end of American democracy," she writes.

InJune, Donald's younger brother Robert Trump unsuccessfully tried to block the publication of the book in court, saying that his niece, who is the daughter of his and Donald's late brother Fred Trump Jr., is subject to a nondisclosure agreement and "not allowed to write the book."

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How this 1950s self-help guru shaped Donald Trump's attitude toward life and business - CNBC