There’s a really good summary here of the book and the key principles behind the art of tidying up.
I found that the most useful idea from the book was that storage is bad. Storing clothes in particular is a form of self deception. I feel so guilty about how many clothes I have, so I “store” them. This book inspired me to just chuck the stuff I’ve kept in storage boxes, even though the clothes are perfectly fine. If I don’t wear them, why keep them? (Guilt. Guilt is why I store things).
She also recommends chucking books after reading them. Her argument is that you can always buy the book again if you ever do actually feel like reading it again (but chances are you won’t). I’m not quite ready for that yet. I do however have a pile of books that I want to read (but never do) or started reading but never finished. I think it would be quite liberating to clear that pile.
Apart from clothes and books, I’m pretty good at chucking stuff. My family, however, keep/hoard everything. Notebooks, cables, toys, magazines, old sheets. You name it, one of them will want to keep it. I normally tolerate it as long as they can find somewhere to put it, for example, in storage boxes that have lain untouched in the attic for ten years. After reading this book, I am inspired to have another go at getting them to ditch all the stuff they’ve been storing/hoarding in the attic.
I’m more at risk of chucking too much, than too little. There have been times when I’ve chucked things of my daughter only to have her search for them some time later while I pretend to have no idea where it has gone. An interesting read is this article in The Atlantic about the opposite compulsion to hoarding which is called “obsessive-compulsive spartanism” and is a serious disorder.
I’m not compulsive about decluttering, but after reading this book I might be (joke).