You read some books at the right time. Something in them shifts the way you think.
It could be that you've been leading up to that shift for some time. Perhaps the book has a completely new idea to you.
I read a lot of books that changed things for me this year. Here's a list:
Braving the Wilderness - Brene Brown Rising Strong - Brene Brown The Subtle Art of Not Giving a Fuck - Mark Manson Sapiens - Yuval Noah Harari The Story of the Human Body - Daniel Lieberman How to Change your Mind - Michael Pollan Why We Sleep - Matthew Walker How Emotions are Made - Lisa Feldman Barret Why Zebras Don't Get Ulcers - Robert Sopolsky Non-violent communication - Marshall Rosenberg Atomic Habits - James Clear This is Marketing - Seth Godin