The short answer: Nobody knows the details—not even YouTube, to an extent. YouTube’s algorithm uses machine learning to suggest videos, which means there are no set rules we can tell you. Besides, Google wouldn’t tell us anyway, as that would lead to people exploiting them.
The metric YouTube uses is watch time—how long users stay on the video. This makes sense because YouTube doesn’t want people skipping around looking for videos to watch, as that’s more work on their end, and less time spent watching.
It’s much more nuanced than just “how long you watched a video,” though. The algorithm takes into account many different factors and ranks them accordingly: viewer retention, impressions to clicks, viewer engagement, and some other behind the scenes factors that we never see. YouTube then tailors these factors to your profile so that it can suggest videos you’re more likely to click.
BTW, if you meet other YouTube playback errors, you can also check this article.
