As we’ve seen, an individual page’s value is computed in part based on its uniqueness and the visitor’s experience; likewise is the entire domain’s value assessed. Sites that primarily serve non-unique, non-valuable content may find themselves unable to rank, even if classic on- and off-page SEO is well-optimized. The engines simply don’t want thousands of copies of Wikipedia filling up their indexes, so they use algorithmic and manual review methods to prevent this.
Search engines constantly evaluate the effectiveness of their own results. They measure when users click on a result, quickly hit the back button on their browser, and try another result. This indicates that the result they served didn’t meet the user’s expectations.
It’s not enough just to rank for a query. Once you’ve earned your ranking, you have to prove it over and over again.