Life changing is open to your interpretation. It can be anything like changing majors to arriving at some serious realization. In short, it caused a tremendous mind shift that led you to take certain decisions that helped you in the long run.
Any reason for which you still remember that book or its contents. Also mention the reason.
The book is also an easy read because the entire thing is told in the form of a father-son travelogue. The fact that the author pulled off a travelogue about the philosophy of science is an amazing feat of exposition. So another lesson is about the value of good communication.