Book review: I have rated this book pretty highly because it is short and tells you exactly how to change negative self talk. However, it misses a star because it doesn't provide any testimonies to show how it might impact people's lives. You have to just believe it will work. Also, it tries to sell a paid program to give you affirmations, which you can find online for free. It does recommend the most effective method for re-wiring your brain is listening to affirmations, but just get a Spotify track or YouTube and a good one will do the same thing. It doesn't say why their app is any better than audio affirmations from free providers (because it's not).
It boils down to: negative self talk is what you think about yourself and your brain is wired to accept these "truths" you tell yourself. It will remember and accept anything you tell it for at least a month. So listen to positive affirmations every day for a month (or longer) depending on how much you struggle with them and your brain will rewire these negative 'programs'. Lastly, your thoughts affect your feelings, your feelings affect your actions. So if you physically want to achieve more in life and not just mentally, listen to positive affirmations to begin your day.
Conclusion: we are, who we tell ourselves we are. There's no universal law of attraction (that the world gives us what we want because we want it) it's because we send our brains the message that we want to be confident, sexy, successful, rich etc and our bodies start to work towards making that happen. Once our mind believes it, that is the truth.