I found this to be an occasionally annoying, but ultimately useful book. M. Kondo has a chatty style of writing, but in a lot of ways it's that sort of indirect approach that helps you get the lessons of the book.
I learned a lot from this book, and used it to wok on my own living situation. While it might be a case the teacher appearing when the student is ready, most people could use a reminder of their relationship to their stuff. Many of the big features are covered here: https://www.onekingslane.com/
live-love-home/marie-kondo- book-declutter/, but there are a few more that I would add.
First and foremost, it's OK to let go of things. Often I found myself keeping things that I meant to get around to, but never did. In a life of limited time, money and energy, being able to walk away from the hobby or book or stuff you would most likely never get around to is an amazing feeling. Sending things on also gives them the chance to improve other people's lives. Clearing out the closet allowed me to have better access to the things I do want, sometimes even to the point of not remembering I had them before now.
Also, clearing things out allows you to get other things that are more what you are now. We think of ourselves as unchanging, with interests that are fixed, but we're not. There's nothing wrong with taking stock of who we are, or want to be now, and making choices based on that.
It is vital to go into the process with an open mind. The style is prone to mockery, especially the personification. But, like using chi as a way to explain good movement, it is a useful viewpoint. A bigger hurdle is hubris of the "I love my attitude problem" sort. Many will declaim that their hoarding is too much even for M. Kondo to fix, or that there are too many things they "have to have." It's important to go into it with an open mind, and with eyes set on some of the benefits. None of us live in a house of limitless room, and most of us don't need Gatsby's closet to get by. There has been once or twice when I wanted something that was gone, but that's more than compensated by a home that has room for life.