That is, until we hit Archetypal criticism. Oh, be still my beating Joseph Campbellian heart. As writers, most of us have heard of the hero's journey; if you haven't, just go watch Star Wars or the Matrix. There, you now understand The Hero's Journey. Okay, maybe it's a little more complicated than that...but just a little.
But of course there's more to archetypes than Campbell had to say about them. Literature of every genre is nothing but swimming with them: the comic hero, the brave knight, the damsel in distress, the dark witch, the wise mentor, the lovable droids, the...wait. Well, you get the picture. In a general sense, they're eternal tropes. You can find them--sometimes completely unmutated--as far back as the Bible, the Popul Vuh, the Qu'ran and the early drafts of Star Wars (Luke Starkiller? Come on.)
And as much as I, as a reader, like things new and different and exciting, there's comfort in the familiar. As a writer, archetypes and tropes are, dare I write it, HELPFUL. They provide a base and touchstone for our readers and for all of our common experiences. We're just as free as anything to mutate them to suit our whims, but in all reality your story just might need to have an evil stepmother. Don't run from it, embrace it! Embrace it and make it yours. So what if your spunky girl just so happens to be red-headed? Alanna of Tortall, Anne of Green Gables, and Pippi Longstocking all were too, and we don't shout plagiarism at L.M. Montgomery or Tamora Pierce. There can be beautiful, subtle distinctions in archetypes and tropes and THAT makes all the difference.
TV Tropes, that delightful time black hole of a site, said it best: TROPES ARE TOOLS. (Now that you've clicked over there and have spent seven hours on the wiki, it's good to have you back. Don't worry, it happens to everyone.) They can be dangerous if used wrong, but used right, they enrich our writing, expand our worlds and--most importantly for me--they are INSPIRING. Heck, every single page in Campbell's "Hero with a Thousand Faces" and every entry in TV Tropes houses a brand new shiny idea for a story.
Do you notice archetypes in the works you read or write? Do you intentionally add things that turn out to be a common trope later? How many people with red shirts have you killed, honestly?
Now if you'll excuse me, I have a few tabs open.
This and more delicious XKCD found here: http://xkcd.com/609/