Wait... Most people have an ending before they start writing?! 

 Oh my! I've been doing everything wrong all these years! 

 * cue hyperventilation sequence * 
* cough * 
In all seriousness (not that I'm ever serious 

 ), I hardly ever know how my book is going to end before I write it. Usually I'll have an idea of the climax, characters, are main idea of the book.
Example:
A trilogy I'm planning on writing right now, which is actually rather over-developed for my style of writing. All I know is that there are two main characters - Jordan and Charis - and I know there are four worlds - Earth, Chevl'Set, Kochav, and Lowinta - and four trees and the four trees enable traveling between the four worlds. 
And as far as the storyline goes, I know that a guy kills another guy and the guy that kills the other guy travels through the four worlds with this girl and I know the climax is the girl finding out that the guy is a * whispers * murderer...
But I don't know how it ends. I probably won't for awhile... Least not until I write it. And I like writing that way. 

 Because, otherwise, I get bored and I don't write anything. Not knowing the ending to my books though is yet to cripple my writing in any way, from my perspective, anyhow, and it's a far more enjoyable way for me to write.
On the other hand, there are some people that cannot write a book unless they outline everything from beginning to end. That's okay too. But if you can write without knowing the ending and, if you find that it's easy for you, then I wouldn't worry about it. Writing isn't really about sitting down and plotting a story, what matters most is the actual story. Forget the details until you have to revise. 
 Bethany Faith
Bethany Faith