I think movies have ruined us all for writing novels. Is the point of a novel really to surprise the reader with hidden twists and turns and gasps and shrieks at what was unexpected? Or are books - and stories in general, I might argue - really about the beauty of how they are written and told?
More than once I've talked with other writers about their stories where at one point they refuse to give something away. But I'll read it anyway, I tell them. I'm trying to to help you out here since you're asking for my advice. I can't help if you don't tell me what happens.
But it's a secret! You won't be surprised if I tell it to you now.
Really? Because as far as I understand it, millions of people keep reading Harry Potter over and over even though they know what happens. The last Harry Potter movie will be a huge box office seller - even though a huge percentage of people who go see it will already know what happens...
When I read Lord of the Rings for the first time I had no idea how Gollum got the ring from Frodo in the end. Someone spoiled it for me a few chapters before I was finished by whispering the end into my ear. I was pretty upset, but looking back I realize that the end wasn't really spoiled for me at all. I still enjoyed reading the rest of the book just as much as I would have otherwise because the book wasn't all about that ending moment. It was about a myriad other things all layered together.
I think we storytellers often overlook one critical thing when it comes to telling a story: CRAFT. It isn't necessarily about keeping secrets. It's about telling the story. We all know how Cinderella ends, but we keep telling the story in a million different ways. We all know Hamlet dies at the end of the play...along with almost everyone else, but it is one of the most beloved tragedies of all time.
Especially keep this in mind when you write queries. I've written one query in my lifetime and I was so blasted scared to give away the end of the book that I think it ruined my entire query.