I don't know much about this Konmari thing. I think it's been around for a while, but got a boost recently due to a Netflix special. I think I agree with it in principle, or at least what I know of it from secondary social media commentary. Minimalism is a worthwhile goal, and so is getting rid of things that do nothing for you other than take up space.
Some people aren't reacting well to the idea of throwing away books though:
Edit 22 Jan: The account has gone private, so the previous embedded tweet is no longer accessible. I'm quoting the original text here:
Do NOT listen to Marie Kondo or Konmari in relation to books. Fill your apartment & world with them. I don’t give a shite if you throw out your knickers and Tupperware but the woman is very misguided about BOOKS. Every human needs a v extensive library not clean, boring shelves
Maybe it's missing the point of decluterring though. The idea is getting rid of things that "don't give you joy", so if having books give you joy, then obviously you keep your books, regardless of whether those books are challenging, difficult, depressing etc. Maybe the point is that you have to be constantly re-evaluating whether the hoarding is a positive spin in your life. (And I say this as someone who has a bunch of books waiting to be read just lying around his room.)
I think this kind of decluttering and minimalism doesn't just apply to possessions though. You should also be looking to give up things like friends, relationships, habits, routines, traditions, and so on, that are no longer net positives or "bringing you joy".
There's sometimes a bigger picture to look at too. Maybe a specific thing doesn't "bring you joy", but your gradnchildren really like seeing that thing when they visit, and seeing them happy brings you joy, so you keep it anyway.
Maybe the bigger lesson is to not rely on someone from a Netflix show to tell you how to live your life. It's good to take advice from other people, but everyone has different tastes and different things can bring you joy. You decide what brings you joy.