I mentioned this book review in another thread, because of some intersting stuff in it about the global financial crisis, but I think it deserves mention in its own thread, in the context of the impact of thinking oncancers.
How Positive Thinking Fooled America and the World

The author Barbara Ehrenreich is a scientist who got breast cancer. When seeking information, she kept being directed to the positive thinking industry. the link will lead you to a summary of her take on the happiness industry, and its social implications. Now, I understand how useful it is to try and see the glass half full. There's a heck of a lot of people encouraging us to do that, and some of them are thousands of years old.

Ehrenreich presents evidence from a number of studies that find that positive thinking has no effect on survival rates. She quotes women who felt they failed, because they tried all the affirmations etc and still didn't beat ther cancer.

For example, a woman who wrote to Deepak Chopra: "Even though I follow the treatments, have come a long way in unburdening myself of toxic feelings, have forgiven everyone, changed my lifestyle to include meditation, prayer, proper diet, exercise and supplements, the cancer keeps coming back. Am I missing a lesson here that it keeps re-occurring? I am positive I am going to beat it, yet it does get harder with each diagnosis to keep a positive attitude."

Ehrenreich looks at the evolution of the philosophy of positive thinking in the UK as a reaction to the bitter pessimism and punitive approach of Calvinism. yes, positive thinking is a hell of a lot better than that.

Ehrenreich examines how the motivational industry influenced post-global-financial crisis sackings. Hyped up business chiefs told staff being sacked not to worry, and during the sacking they were reminded that they were, in fact, infinitely powerful, if only they could master their own minds.

I guess a significant factor is that this motivational optimism is pointed at the individual, and the right of the individual to succeed, or even to maintain their positive view in the face of evidence to the contrary.

The significance of the importance of facing the negative can't be understated. Ehrenreich points out that in 2003, a US government official called Armando Falcon warned the White House that companies like Freddie Mac and Fannie Mae were backing far too many dodgy mortgages, risking financial collapse and "contagious illiquidity in the market". Did the White House look at tightening up regulations? Nope. They tried to sack Falcon. He was just being "negative".