This is a self-help psychology book that I've really been able to use.
It teaches cognitive therapy -- the basic idea is that your thoughts create your emotions, and that by changing your thoughts, you can change your emotions, and thus change your moods.
It's not about Pollyanna positive thinking. It's about eliminating distortions in the way that you think.
Although the author claims to have seen almost instantaneous breakthroughs in some of his severely impaired patients, my experience was that the book's methods worked best not to make major changes, but to be able to deal better with small-scale everyday problems.
For example, before reading the book, if I was expecting someone to call or email, and they didn't, I was likely to become worried that they were mad at me, and then I would start wondering what I did to offend them, and I could become quite convinced that I had done something wrong.
Using the cognitive therapy tools, I can now usually recognize that what I'm doing is spinning a fantasy that exists inside my own head and that may not have any relation to reality. This helps me cut short the obsessive cycle of ruminating about my faults before the cycle takes on a life of its own.
It's interesting, when I do this, how often it turns out that the reason the person didn't email or call was due to a misunderstanding (they never got my messsage) or for some other reason that had nothing to do with me at all.
This may sound like it's just common sense, but it can be easier said than done, and the book gives specific techniques that help put it into practice.