People who read a lot and watch a lot of movies are ultimately influenced (maybe you can say "polluted") by them. On the other hand, art is a series of builds and revisions working on old themes, as old as Gilgamesh and Aeschylus. Shakespeare was an unapologetic thief of plots. Most other "famous" writers use other writer's or playwright's plots, imagery, even character types. I suppose you could lock yourself up in a cabin in the woods, without any media, but then you would be even more in the dark about the pulse of interests going around.Many cases tell us that a book may take a year or two to write and perfect, and then another year (or two) to shop around. Let's say 4 or 5 years. So even if you did write a book that echoed something of another book, you might be 4-5 years behind that other writer. Look at how many "fantasy" books about teenagers and their pet dragons are shopped around. Those people are not necessarily plagiarizing each other, though some may have been inspired, informed, or owe a debt of gratitude to an earlier book. I like to consider that "Cold Mountain," and "Oh Brother Where Art Thou?" and according to Wikipedia, nine more pages of books and film are based upon "The Oddessy," one of the oldest stories around.