The details of Google’s search algorithm are not disclosed to the public. Google’s public statements, Webmaster guidelines, and patent filings give us some general insight into the overall approach of its search algorithm. However, the details are closely-guarded secrets. For example, how does Google’s algorithm treat a title tag how much weight is afforded to this important component of a webpage? Is it 30%? 20%? Even if we did know, Google’s search algorithm is subject to constant tweaking and updating. So, we know that a webpage’s title tag is important, but the actual numerical importance within the Google algorithm we will never know.
So if the relative importance of different ranking factors isn’t publicly disclosed, how do we even know which ranking factors are more important? The answer lies a little bit with the search engines’ public statements, a little bit with logic, a little bit with experience, and a little bit by the consensus developed by SEO professionals and hobbyists.