It's interesting how a person who studies mental health can write a book that completely ignores people with mental health issues or neurodivergent brains.
In fact, this book only seems to address middle class people with rather stable lives and a few privileges, who are also in a committed relationship with our system. (I say this, because motivation is mostly focused on getting things done, without really asking how to deal with the feeling of things not being worthy of being done. Like ....in our capitalist society the majority of jobs is only necessary because of capitalism. They have no higher purpose then to feed the person doing the job. So, people who want to gain something by reading this should be okay with possibly leading a life that has no other use than to keep capitalism alive.)
Don't get me wrong, most tips are good for SOME people. And they are scientifically proven. But keep in mind that science, until lately and in some cases still, focused on the middle class, white, dya cis allo-hetero, neurotypical and abled male.
So ... whoever might not check all those boxes might find, that their life's reality is only partially taken into account - or not at all.
And then there's also the issue of personal taste. Like ... I assume it's not due to my disabilities or my mental health that I UTTERLY dislike constantly happy people. Okay, then drain a lot of energy, that might be partially linked to my neurodivergence. But in the end this is probably just my personal taste. But even that is an issue here because the book seems to value these nuisances of humans, while it doesn't like pessimism. (It even links pessimism to anxiety, which is a bit odd, because personally I feel if I know what CAN go wrong, I'm more relaxed when approaching something. But again, I'm not part of the group that science likes to focus on.)
So ...yeah, the book is probably immensely helpful for some.
Just not for all, because humans come in all varieties and personally I was not addressed here at all.