Just how powerful IS positive thinking?

But what about survivors like Mark Herzlich, Lance Armstrong - and even Congresswoman Gabrielle Giffords, a gunshot victim whose husband Mark Kelly attributed her recovery to more than just medical care?

"Please continue to keep Gabby's thoughts and prayers in your heart," he said. "It is really helping."

"She survived because the path of the bullet - that's why she survived," said Sloan. "If the bullet had hit something vital in the brain, she would not have survived."

Positive thinking, of course can lead to good things ... a better mood, increased happiness, and - this is key - making a patient more willing to endure the rigors of mainstream medical treatment.

Many of the participants in the Avon race to raise money for a breast cancer cure owe their lives to their determination to fight through the pain of chemo and radiation.

"It's almost better than medicine because if you have a good outlook, your energy is better, you feel like doing things," said Lawanda Fountain. "You don't have sad thoughts where you are and have your own personal pity party and there is no one there with you."

But author Barbara Ehrenreich, who went through a grueling bout with breast cancer, resented pressure to be cheerful.

"I didn't want to be told how to feel by somebody else," Ehrenreich said.

She recovered, she says, simply through good medical treatment. But the experience experience made her realize just how pervasive the belief is that positive thinking causes positive results. She characterized it as, "If things don't go well, if you get sick, or if you lose your job, or fall into poverty, it must be your fault because you weren't sending the right thoughts out into the universe."

"Well, what's wrong with that attitude? A lot of people have it," said Braver.

"It's wrong because it's not true!" Ehrenreich laughed.

Her book, "Bright-Sided" (Macmillan), argues that the relentless promotion of positive thinking has undermined America.

For example, she cites bestselling authors who guarantee all sorts of success to those who have the right attitude. Or religion: They promise prayer can make illness vanish. "And one day when I went to go pray, the tumor wasn't there," said one church-goer.

"Is the alternative to positive thinking to be negative or pessimistic or fatalistic?" asked Braver.

"The alternative is to try to see the world as it is more. Realism, I would call that," said Ehrenreich.

But cancer survivor Leigh Fortson argues, "To me, reality is in the mind of the believer. That's what reality is,"

Fortson did undergo traditional medical treatment, but she is also a true believer in other solutions, including belief.

"A big part of my journey was working with my mind, and that was as much as anything," she said.

Fortson interviewed a few dozen survivors of cancer, heart disease, MS - all of whom relied on alternative treatments, sometimes exclusively.

She recounted their success stories in her book, "Embrace, Release, Heal" (Sounds True).

"And the doctors who say, 'Sorry, there's no evidence of that?'" asked Braver.

"There is evidence," replied Fortson.