You're saying youtube is good at suggesting things you might actually be interested in, that reflect your actual viewing habits?
I would say many of my video recommendations are ridiculous, they're so obviously not what I would want to be looking at. Put it another way: I'm watching videos about fertilizing lawns but they're recommending videos about replacing lawns with gravel. I'm watching videos about travel destinations but they're recommending videos about personal travel's harmful impact on the environment. Those examples are for illustrative purposes only, but you get my point. The "suggestions" are often clumsily obvious attempts at redirection. I'm watching a video that's very critical of Mike K., but my top recommended video is called "Ten Reasons Why Mike K. Is Awesome".
Web ads in general are also very curious things. I can spend weeks intensely searching on a particular project, watching videos, reading advice blogs and message boards, and making online purchases of related supplies and/or equipment... and yet I NEVER see an ad related to what I'm doing. When I say "never", I mean absolutely never. Like not even one time will I see a relevant advertisement related to the thing that has been dominating my online activities for weeks or months in a row. But I'll see recurring ads seemingly trying to tempt me into all sorts of unrelated directions.