If I can only pick one, I think it would have to be "The Diary of Anne Frank."
I read it when I was 13, back when I was still living in Portugal. It was the first book I read that opened my eyes up to a world of books beyond fairy tales and imaginary lands; and it has stayed with me ever since, even if imaginary worlds are still my favorite
I'm pretty sure that back then, I didn't fully grasp the importance of the events she relayed in her diary. It's okay.
What I did know when I got to the end, was that it was no ordinary book. I knew her story was one people needed to know, and I was in complete awe.