Having used this phrase with a family member who weakly agreed to do something she really didn't want to do (and was then utterly miserable for it), I had a quick google to see if there was a book with the title "the power of no".
And lo and behold, there are several books with this title! 😃
Has anybody read any of them, by any chance? I like the look of the one by Abbie Headon, from 2019, or Becky Kildea.