I read it, did the work, and it is life changing. People with a pessimistic outlook are much less happy than people with an optimistic outlook. The book teaches you how each type thinks (for example, optimists think everything good that happens to them is personal and permanent and every bad thing that happens is impersonal and temporary. Pessimists are the opposite). The book then teaches you essentially a cognitive behavioral therapy technique to retrain your brain to think more like an optimist. It’s work but so worth it especially if you ever experience anxiety.