Google was founded on a simple principle — some web pages are more important than others.
How is that importance quantified? Ideally, it’s based on the fact that people think that page satisfies their questions about the topic better than other pages.
Google changed the face of search technology by evaluating a web page’s importance by the links that pointed at it, both in sheer number and by how much Google trusted the sites those links came from.
But the web has changed radically since 1998. While plenty of people can start a website or blog and link to things they like, the majority of people vote for things they like via social media sharing.
That makes social sharing a great signal for a search engine to use … but Twitter and Facebook are not exactly cooperating with Google. And until recently, the web page itself — and not the writer — was still the central part of the story.