What I've always been taught is that there are three basic stories:
man vs. man, man vs. himself, man vs. environment. But such distinctions
are false and fairly misleading; they generalize but do not perceive.
There are as many stories as there are people. If you take someone's
life and spin it out in a book or a movie, it's 100% different from the
life of the person across town. If you base your stories simply on plot,
then sure, you're going to run into problems. If you base your story on
character, and make your characters distinct, this problem doesn't occur.