Which book fundamentally rewired your decision-making?

I’m looking for the books that did more than just tell a story—the ones that actually shifted your worldview or taught you a mental model you now use every day.

Whether it's about systems thinking, psychology, or a timeless classic that changed how you communicate, what is the one book you constantly recommend because of the lasting impact it had on your brain?

I’d love to hear the "why" behind your choice.

Thanks!