There are any number of people out there who believe in positive thinking. I have extensive experience in the computer industry, and when you are a programmer you cannot afford to practice positive thinking. You have to think analytically. You have to anticipate anything that can go wrong with the product. You think positive, you fail to anticipate problems, you create a product that does not work.
Positive thinking was quite popular in the baby boom generation, but is largely sneered upon in Generation X. As a gen-X acquaintance of mine said on the internet, "Fucking optimists." You talk to these people about positive thinking, they think you're an idiot. They tend to be a fairly analytical bunch; and many of them have had success in the fields requiring analytical thinking, such as the computer industry. That is because, once again, that industry requires analytical thinking; and people who tend to analytical thinking are suited to the profession.
Positive thinking can in fact work as advertised at times. If you are positive, you are more likely to "win friends and influence people" than you are if you are negative. It is an attitude you want in salesmen; but it is not an attitude you want in engineers. People who think in different ways will not usually get along; however they need one another. The engineer needs to market his product. The salesman needs a product to sell.
Of course analytical thinking can go wrong as well. One place where it completely fails to apply is in man-woman relationships. The person becomes perfectionistic to the point of only seeing the flaws in the partner while failing to recognize the partner's good qualities. This makes everyone miserable, including himself. He becomes a nitpicker; a controller. He keeps picking on whatever he sees as being wrong with the partner - however good the partner may be - while failing to see the good in her. He creates a hell for the partner and for himself.
I once knew a man with engineering and military background who would make his wife spend 6 hours a day cleaning the house and would come at her with fists whenever he found a speck of dust on the floor. This is misapplication of thinking, and it worked against his best interests. A speck of dust on the floor will not kill your family. Abusive behavior stands to destroy it. And of course, in the end, it did.
Another misapplication of analytical thinking is in culture and the arts. These fields do not require analytical thinking; they are about producing things of beauty. When Jewel came up with a book of beautiful poetry, she was savaged by gen-X media. In fact her work was far better than anything that these people produced. Quite simply, such people should not be in the arts business at all. They should stick to things that they're good at - things such as programming - and leave the arts for people who actually produce things of beauty.
When I attended an avant garde poetry reading with a magnificent visual artist, she told me, "I hope you never write that way." I do not. She was my inspiration, not them. I ended up writing a poetry book for her that made me - and her - the talk of DC. There were many people who attacked her work; but it was far better than anything that any of them have produced themselves, and I dare say it was the most beautiful work that has ever been produced by a woman.
Different endeavors require different kinds of thinking. It works to be positive in sales, but not in engineering. It works to be analytical in developing software, but not in running relationships or in producing art. By all means be positive to your clients, and by all means be analytical when developing software. But do not go around nitpicking at your partner, and don't go around turning culture and arts into cold cynical abominations. Keep to fields such as programming and leave the arts to people who have interest in producing things of beauty.