It also learns if you like rare music and somehow finds networks of people/videos that you resonate with. Every day I discover something interesting that I wouldn't have thought to click on (artwork + name), by just letting YouTube autoplay. Classic Zambian rock, Nigerian disco, rare 80s Italian or Japanese electronic music, some brand new French dub guy.

Invariably there are a bunch of other people commenting about how "the algorithm" surprised them again. There isn't a single algorithm.