I'd say my favorite book is Umberto Eco's "The name of the Rose". It's really hard for me to say "my favorite book" because I love literature, but I pick this one because it was my first adult reading.
I was fourteen when I decided to face the challenge, driven by the movie with the great Sean Connery, as well as by my interest in History.
It was, of course, very hard, but it only teased me to struggle. At the very first paragraph I was faced with the reality of no understanding at all. I reread once, twice, three, four times. I got mad and abandoned it. I came back to it after some minutes and failed to get it again and again. Then I breathed and realized there was actually some comprehension on my mind, I simply wasn't sure. So I decided to carry on, only to check I had grasped the meaning in the following paragraph. I thought it could be just out of luck and tested this tatics of confirming comprehension once more. It worked again. That's when the reading gained me!
It became a kind of game. I read, stopped to "feel" what my understanding was, took notes of it on the margins - which became a forever must do when I read - confirmed the accuracy in continuation. I remember thinking the author was a type of sorcerer who could read my mind in advance - it was just much later I found out it's called Semiotics. I remember thinking he was my invisible friend who embraced me in a secret dialogue.
Umberto Eco taught me how to read.