I've seen too many people cycle through the same "classic" recommendations, but the one that keeps showing up in real, lasting impact is *The Alchemist* by Paulo Coelho. Not because it's the most complex, but because it's the one that sticks with people. It's not just a book—it's a mindset. Every time someone comes back to this question, I think of how many lives it's quietly shaped. It's the one that doesn't just get read, it gets lived.