It's scary to think their is another human with a near identical watch vector as my own.  By recommending videos from similar watch vectors don't we just create ever increasing echo chamber type clusters?,(reply>), Echo chambers are indeed a potential bottle neck of collaborative filtering recommender systems. It is an area of active research. For example, this article discusses augmenting movie recommendations with top ranked films from adjacent clusters, on top of recommendations from the user's cluster. Much of this process is complicated by the fact that your similarity calculations are often done on "latent features"," that is information that isn't directly observable in your data. <a href=""https://towardsdatascience.com/overcoming-echo-chambers-in-recommendation-systems-using-movie-ratings-3686f50fc053"">https://towardsdatascience.com/overcoming-echo-chambers-in-recommendation-systems-using-movie-ratings-3686f50fc053</a>"