Now, having only just watched the preview of Avatar, I can see that there might be some very broad similarities, but only in the same way that you can see broad similarities between, say, Les Miserables and Crime and Punishment. Sure they're both broadly about redemption, and there's some fairly common tropes about the nature of humanity in the face of moral dilemma, but the approaches to the story are fairly different.
It's got me thinking, though - one of the big risks you take whenever you put something creative 'out there' is the risk that someone's done it first. It's something that will, I suspect, happen to most writers at one point or another.
I remember vividly one particular night in 2003 when Imogen and I were living in Brisbane and I was in the final editorial stages of Fireshadow. About three months before the book was due for release, I read David Metzenthen's Boys of Blood and Bone, which had just hit the bookshelves.
Imagine: There it was - a YA story set in the World War One (mine was in WW2), with two protagonists both in their upper teens (same as mine). One has gone off to fight the war (same as mine), while the other is a contemporary youth struggling with that period immediately after school (same as mine.) The chapter structure was the same - each chapter alternating between past and present with the present narrative told first. The similarities - especially across the first half of David's book - went on and on. The breaking point for me was when I got to the point where his protagonist goes off overseas unknowingly leaving his lover pregnant (Same as mine). That was when I yelled an obscenity and hurled the book across the room.
I couldn't believe it. At that point I'd been working on Fireshadow for about five years. At that point I'd never met Dave Metzenthen. We'd never spoken, lived on opposite sides of the country and yet had managed to come up with two remarkably similar books, on similar topics and with similar narrative approaches, just six months apart from one another.
But it's the nature of ideas, I guess.
According to Stephen King (I'm paraphrasing here) a lot of the time writers have no idea where their ideas come from, or what particular forces are shaping the way they see the world, but it's fairly probable that if an idea has occurred to you, then somewhere, someone is working on something very similar. And when it happens, it's awful. That night reading Boys of Blood and Bone (which is a book I love, by the way) was one of the most horrible moments of my life.
I think the secret, though, is to make sure you put a lot of yourself and your own world into everything you create. That's where the differences lie. Someone might have the same idea as you, but as long as you make your story your story, chances are that the points of difference will shine through and lend your work the unique elements that all creative works need.
That said, if James Cameron wants to cut me in for a percentage of the royalties, I'm willing to talk...