I was going to name Washington Irving's 'The legend of the Headless Horseman' at first because, reading that at about age 10 I had my first connection with literature. It's not exactly a startling insight but there's a part where Ichabod is going home through the woods and all the ghost stories he has heard that night come back into his mind just when he doesn't need to remember them. I thought, 'Wow, that happens to me'
Then around the same age I read Treasure Island. I'm guessing this would be a very popular choice. What young boy wouldn't put himself in Jim Hawkins' buckled shoes?. Images from that book have stayed with me for 40 years. The raw horror of Jim, trapped at the top of the mast with Israel Hands climbing up after him, knife in his teeth and murder in his heart. I remember feeling real sympathy for poor Ben Gunn longing for cheese while he lived among untold but useless riches. Then there was the confusion engendered by Long John Silver and his shifting allegiances. Jim the son he wanted and him the father figure Jim wanted. A truly magical book.