This also ensures that you are staying on the site longer, come back more often and have a positive imagine of the site because you like what you see.

It also increases the likelihood of you engaging with the content shown. Comment, like and share.

Every now and then the algorithm takes a guess and will show things it usually would not show, which serves as a test. Do you engage with it, is your stay terminated or do you ignore it? Based on that it adds to your profile for next time.