Halfway through this book, I was still going to give it four stars. There is some good science in the first section, explained in a way you can make use of. I dropped to three stars, and maybe to two, by the end.
Perhaps it was when he listed, on page 59, health habits we needed to acquire.
We should watch our salt and drink more water. We should eat more vegetables and fewer fats. We should take more vitamins and apply sunscreen. The facts could not be more clear...
Except, of course, that all six are questionable. Even the strongest of them, the vegetables, is a statistical average, not a given for everyone.
Or it may have been when he lauded Rhode Island Hospital for showing its commitment to safety by sending everyone to a day-long workshop on teamwork. I felt sorry for the poor bastards - I've been to that sort of thing for thirty years, but have never seen one stray number to suggest that the method works. A psychiatrist friend who got a special fellowship to study and teach teamwork was among the worst at actually listening to team members I have ever seen. Perhaps he wrote the curriculum for Rhode Island Hospital, eh?
But by the time he was quoting Rahm Emanuel's comment about never letting a crisis go to waste, noting approvingly all that Obama had been able to accomplish, I realised that Duhigg just believes the conventional wisdom of what people in his circle tell him, without stepping back in any way. That might not invalidate his understanding of how the power of habit was important at Alcoa, or Montgomery Alabama, or the London Underground, but it certainly calls all these examples into question.
He likes a nice, tight narrative where the example he chooses illustrates his point about habit without loose ends. He occasionally mentions that it's more complicated than that, but... And the "but" is always that his little anecdote about the power of habit is the overwhelming factor. Regarding Montgomery and the boycott, no less an authority than Thurgood Marshall said it was unnecessary, but Charles Duhigg dismisses that.
Experimental evidence - now including fMRI's! - suggests that you have a better chance of losing a bad habit if you replace it with something else. Sometimes it's hard to find what you are really craving and what a good replacement would be, but think about it hard and try some different things. Next, It helps if you have a plan what you will do when the hard times come, as they inevitably will. There. That's the book. The rest is cheerleading for people who like anecdotes aimed at a somewhat higher educational level than an Amway speaker. There's no hint of firing you up, here, just patient explanation.
Get it from the library, as we did, and read the first 150 pages. It will inspire you to try a few things, and give you good tools for getting started. Maybe that is worth four stars.