One thing that outrages many people that know me is that I am proudly an opponent of positive thinking. It's not that I think positive thinking is bad, it's that I think positive thinking is useless without negative thinking.
The universe is nowhere uni-polar. You cannot have a north pole without a south pole. You cannot have a positive charge without a negative charge. You cannot have an up without a down or a light without a dark. In a world without opposites, there would be no energy, no organization, no motion, and no progress.
I am an engineer. Engineers are the polar opposite of marketeers. Marketeers sell an idea, but engineers balance the idea with reality. Someone says, "Wouldn't it be great to offer flights from London to New York with a flight-time of only 3 hours. Yes, it is possible to do that. The Concorde did it for a while. However, the Concorde couldn't have done it without engineers thinking negatively. They had to think about all of the things that could go wrong with a jet flying with passengers at that speed. Where would it land if it had a mechanical failure? What stresses would be put on the passengers? How well would the design put up with the stresses it would experience? Literally thousands of negative thoughts went into making the Concorde a reality!
However, not enough negative thinking was put into the economics of the Concorde. Not enough negative thinking was put into the environmental factors of the Concorde - the carbon footprint, the noise pollution, and more. Without enough negative thinking the Concorde had to be grounded.
Engineers thought about all of the negatives in the design of the Space Shuttle, but the bosses above were more concerned about appearances and portraying the project as successful. The engineers were ignored and on two flights the crew were lost.
Negative thinking is as essential to success as positive thinking. Positive thinking is like a bird with only one wing. It won't fly long.