The title of the book gives the impression that it's a self-help book. It's more of a psychology book explaining how people can make mistakes, think they are right, and honestly believe that. A good example is false memories. How often have you said, "I could have sworn I did that." You see the event in your head, yet evidence shows it didn't happen. You rationalize it ("someone must have moved it") instead of accept the most obvious answer ("I was mistaken in thinking that I did it").
The books goes even further into big mistakes that people make and refuse to admit, such as in the criminal system where suspects are locked away for years ("I know he's the rapist so I'll interrogate him for hours until he finally confesses") until DNA finally proves their innocence. Fortunately for most people, they are not making mistakes that means life and death. The book contains many extreme examples. Still, this is great book to read to understand and recognize your own mistakes. For example, maybe a friend asked for a favor and you said no. Initially you felt a little guilty for saying no. Then you start justifying the answer, "She wouldn't have helped me if I had asked for a favor. She's always looking for someone to do her work." So that guilty feeling goes away. It's a rude awakening to realize how your feelings have completely changed -- you went from feeling a little guilty to thinking your friend is selfish and lazy.
This book didn't have any new information for me. I've already read "The Power of Habit" and learned that it easier to rid a bad habit by replacing it with a good habit, such as replace "eating sweets" with "eating an apple" rather than simply trying to stop the bad habit. I've also read "The Willpower Instinct," which explains conditions that helps you strengthen self-control (like building up your willpower a little at a time like a muscle). This book also provided other well known techniques for learning something -- observe, perform, and teach. If you had ever tried teaching others, you would have found gaps in your knowledge of the topic as soon as the learners started asking questions. As you find the answers to those questions, then you really become an expert in that topic. If these concepts are new for you, then this book would be useful.
The book lacked a tight integration of all the concepts into a step-by-step program. It approach varied -- sometimes it was about "try mediation... do this...." Then it switched to information, like how your brain works and how your willpower can be depleted. Then there's a little of both, like good behaviors are used to justify bad behavior ("I exercised today so I'm going to reward myself with some chocolates"). I think you need to read only one chapter a week to absorb the information and practice it for a few days before moving on to the next chapter.