Ron Galella / WireImage / Getty Author of The Secret, Rhonda Byrne

It's not as if Oprah created the theory behind the best-selling self-help book The Secret, written by New Age guru Rhonda Byrne. But by promoting it on two episodes of her show, she may have given it a dangerous level of credence. The book's central premise, the Law of Attraction, is that positive thinking is the route to obtaining what you want in life, while negative thoughts will cause bad events to occur. But when Oprah's producers received a letter from viewer Kim Tinkham  who had received a breast-cancer diagnosis shortly after the shows aired  they were alarmed by how far she had taken the inspiration. Tinkham wrote that she had decided to forgo chemotherapy, instead choosing to follow the book's advice literally. Oprah brought Tinkham on the show to set her straight and urge her not to "ignore all the advantages of medical science." Tinkham, who went on to follow another New Age regime laid out in a book called The pH Miracle, died in December 2010. Ultimately, Oprah stood by her position that the Law of Attraction can effect positive change.

See "The Secret of Success."

Next The Letterman Feud