Not so happily ever after...

I just finished a book that was 412 pages long and I was LOVING it until about the 410th page when something unexpected and totally sucky happened! I was so pissed and angry at the author for writing the story like that, and for almost ruining the whole book for me. Why does it have to be so dramatic in the end? I feel the same way about the new Harry Potter book coming out this summer. If Harry dies in this book I won't even read it. How can he be "the boy who lived" if in the end he's ultimately going to get it?