~Thanks to BBaka for the RotK quote~
Sam: It's like in the old stories Mr. Frodo. The ones that really mattered. Full of darkness and danger they were. And sometimes you didn't want to know the end - because how could the end be happy? How could the world go back to the way it was when so much bad had happened? But in the end, it's only a passing thing - this shadow. Even darkness must pass. A new day will come. And when the sun shines, it will shine out the clearer. Those are the stories that stayed with you - that meant something. Even if you were too small to understand why. But I think, Mr. Frodo, I do understand. I know now. Folk in those stories had lots of chances of turning back, only they didn't. They kept going... because they were holding onto something.
Frodo: What're we holding onto, Sam?
Sam: That there's some good in this world, Mr. Frodo. And it's worth fighting for.

I'd explore further on this, but I believe it speaks for itself.