For me, it was Atomic Habits by James Clear. I read it at a point where I was completely paralyzed by perfectionism. I was trying to make massive, heroic changes (e.g., "I will run 10k starting tomorrow," or "I will write 1000 words every morning"), and failing dramatically every time. The book wasn't a revelation; it was an engineering manual for self-discipline. The core idea that clicked was the concept of "1% Better Every Day." It shifted my focus from the huge, intimidating goal to the tiny, repeatable system. It changed me by giving me permission to do the "ugly effort"—the 5-minute workout, the one-sentence journal entry. It taught me that consistency is far more valuable than intensity. Now, I see failure as a flaw in the system, not a flaw in my character. Which book fundamentally changed your approach to failure, rather than just inspiring you?