FWIW, I think sacrifice is the unifying theme that connects every work of fiction that I have ever loved.
Here, also. The willingness to sacrifice things you want in order to do the right thing is a theme that keeps coming up in my work.
Without the characters sacrificing something a work feels hollow to me, like all the struggle and conflict were for nothing. It's just 'A person does something, and they get everything they want without having to lose anything and without having to change at all.' What's the point?
I'm not saying they have to sacrifice something big, necessarily - it can be as small as sacrificing their ability to go out clubbing all the time to spend time with a neglected loved one. But they have to lose something to gain something else, because that is how life works. And even in fiction, we have to tell the truth about how people are.
Edit - I think there also may be confusion about what I mean when I say 'sacrifice'. I simply mean the character must lose something, even if they gain something better out of the deal. I would say the vast majority of books have a slight sacrifice in them, even if it's a sacrifice of something the character hates and doesn't want. For example... Twilight (shudder) Bella DOES lose something - she loses her humanity, and she gets married when she doesn't want to so that she can. She gets what she wants, but she has to give up something else in order to do so. It's not a true sacrifice, but it's still a sacrifice.
It happens in real life all the time, too.
I want to be a published writer, which means I have to give up allowing my friends to come round without warning all the time, and a lot of my social life. I give up one thing in order to have something I want more.
I want some new clothes, but I have too many, so I have to get rid of some of my old clothes. I have to give up something in order to have something else.