Revelation

So, I was reading one of the books from the same series as the Da Vinci Code. And when we got near the end of the book, they finally started to reveal the identity of the villain. And I realized who he was moments before they actually told us.
That right there is some genius writing: to help the reader come to a realization moments before they actually give the answer to you. The timing of the clues has to be absolutely perfect.
If you figure out the mystery too soon, then the suspense isn't there for half of the book.
But it makes the reader feel so clever if they can figure it out for themselves too.
Although some writers don't want you to know until the answer until they can give you the dramatic reveal. And shock factor can be exciting too. I remember the first time I read Harry Potter, near the end of the first book. We got to the point where Harry reached the end of the obstacles before on the way to the mirror, and the chapter ended just before telling us who Voldemort's servant was. I couldn't wait, and had to flip to the next page, just to find out. That was a long time ago, but I certainly didn't guess who it was.
This can sometimes backfire if it's not done well though (For example, Amon in Legend of Korra. I was convinced that he was we'd met him before, but he ended up being some totally mysterious person who we couldn't possibly know about).