As the title indicates, the book discusses the ways and benefits of thinking negatively. Basically, when a person is feeling anxious about something, one way to combat this anxiousness would be to think of all the negative possibilities of the thing and to plan to prevent (or to know how to react to) those negative possibilities. This way, the person can feel more in control of the situation, and can often react well to obstacles.
Obviously, the things discussed in the book don't apply to everyone, and many of them don't apply to me. However, when reading the book, I did find some parts of it to be important to me. For example, the book describes procrastination as a self-handicapping action, where the person handicaps themselves so that if they fail, they can attribute the failure to "doing the task last minute," rather than their own inability. And although this may seem like a working strategy, it definitely has many drawbacks, including being constantly behind schedule, being viewed as undependable, and— obviously— having poor quality work. So next time I want to procrastinate, I shall think about the negative consequences of doing so.
Also, part of the book talks about how confidence and positive illusions can have negative effects on a person's performance. I should watch out for them in the future.
Overall, I think this book an interesting book for quick-reading, and at the same time one that contains helpful information. Read it, especially if you consider yourself as a pessimist.