The principle that online users are increasingly living in a bubble that echoes their own opinions. This is because search results from sites like google tailor results based on your previous search history and browsing history. Sites that you are more likely to visit rise to the top of search results in the name of convenience. A side effect is that every time you search, you are less and less likely to come up against links that may challenge or contradict your existing views, which results in people's bubbles becoming more and more reinforced.