At the Techonomy conference earlier this week, Facebook Director of Product Adam Mosseri explained exactly what goes into that process, and it's a lot more complicated than we could have ever expected. Adam says that the average person has the potential to see about 2,000 Facebook posts a day, but probably only sees about 200. As PC Mag writes:
However, Adam says that they are always trying to improve the success rate of the algorithm to pick posts you'll like, and that they take into account three goals when they are deciding how relevant a piece of content is: First, to connect you with friends and family, second, to provide information about the world around you and third, to entertain.
"Mosseri said the company uses a blend of automated ranking and manual curation by individual users to determine the feed. At the heart of this is a ranking algorithm that looks at all the content it could show, and determines what to show based on the things you like."
When it's ranking content, Facebook ranks content based on whether you like, comment, share or spend time with a post. There is also a "feed quality control" panel scattered across the world that manually ranks stories, which Facebook then compares against the algorithm rankings.