ABC News consulted a range of professionals about the claims in the book. Dr. Richard Wender, president of the American Cancer Society, has concerns with the implication that we can create disease or heal ourselves simply by our way of thinking. "I want to be very clear that there is no evidence that people attract cancer by their thoughts," said Wender. "Not only that, I know patients who went through their treatments anxious as can be, convinced the whole time that they would never make it, who today are completely cured because they got good treatment in a timely way."
Wender also worries that people following the guidelines in "The Secret" may reject helpful therapies in favor of positive thinking.
"If some person chose to strictly follow the steps in this book, there is a risk that they could die needlessly," said Wender. "If you have a disease where we have treatment that we know can cure you, and you opt not for that treatment, you will die."
Even Proctor thinks "The Secret" might have gone a bit far on this particular point. "We hear people say, 'Well, we just have to think and then we can get rid of cancer. I don't know anybody that says that. I certainly don't say that. I think if there's something wrong with the body you go to somebody that understands the body and take treatment for it."
Other contentious views include the idea that our lives are entirely a product of our thoughts. Specifically mentioned: If you think you're thin, no food can make you fat. Another claims that if you ask that checks come in the mail instead of bills, eventually you will get them.
"Well, who can argue that thinking positive thoughts and setting big goals is better than thinking negative thoughts and having small goals," said Pete Peterson, a former secretary of commerce. "But to think that wishing makes it so -- I call it a dangerous childhood fantasy."
"Success in business is not about wishing, it's about earning it the old-fashioned way," said Peterson. "Too much planning of your life is a dangerous idea, because so much of success is determined by random, what I call dumb luck events."
Valerie Reiss, the spirituality editor of the Web site Beliefnet, says "The Secret" has been spilled for a while. "It's something that I'd heard a lot before … the idea that we create our own reality."
But that isn't her only criticism. "I mean, the idea we can sort of become our own God, in a way, and tap into this energy force, is very arrogant." Reiss also believes that the book's appeal is due to its clever marketing. "I mean, [it's] genius … [to] call it a secret. Everybody wants to know a secret."
For yet another perspective from Brian Green, a noted physicist at Columbia University, also offered his professional opinion. "If by law of attraction, they have this notion of having a thought and it attracts like thoughts, I can assure you that quantum mechanics has nothing to say about that."
On its back cover, "The Secret" boasts that great thinkers like Plato, Galileo, Edison and Einstein all knew a secret that the rest of us didn't know. Green doesn't buy it. "Look, I've never met any of those guys," he said, "but I have zero evidence that any of them would've held on to any fundamental secret about the world and not shared it."