First I need to say that I haven't read the book. However, I came across the idea of the law of attraction a lot, but what I am about to say might not directly refer to the book.
I think our thoughts have a great influence on our lives, more significant than we might think. :-) With negative self-talk, we can block many paths. With openness and readiness for something to happen, on the other hand, we can see opportunities and act upon them. So it's mental preparation.
I saw this idea taken to an extreme though with which I do not agree anymore. It's not enough to think the thoughts you also need to work towards your goal. I also do not like that it seems to imply that if something terrible happens to you, it is your fault as you didn't follow the law of attraction yet. Kind acceptance in those cases seems to be a better first step.
I have seen this in other spiritual practices as well. There is a truly helpful core to the practice, but when taken to the extreme, it becomes spiritual bypassing.