system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are Youtube recommendations so awful?
gpt
So awful in what sense?

YouTube tries to guess what you might be interested in, but the problem is that this is done by a complex computer program. It is, crucially, not human and thus unable to actually think. The exact algorithms used are not publicly known and are tweaked continually anyhow, but YouTube doesn't have much to go on.

YouTube can't "know" what is actually in a video, but does know about text. So it tries to guess what a video might be about based on that video's metadata, and this includes:

* the video title
* the video description
* the tags
* any closed captions that may be available
* other user settings, such as category, location, etc.

This has no chance of working properly if video uploaders are dishonest, which is one reason why videos can be taken down for "spam, scams and misleading content" if the metadata is designed to try to game the system (never put tags in your video descriptions, that's a common reason for video takedowns).

It also stands no chance of working at all if people don't bother with descriptions and tags, and if they use vague non-descriptive titles.

Even if the metadata is good, there's no guarantee a computer program will understand it. For example, given a title like *Maria and Sandra Make Up*, would a computer program recognise this as a beauty tutorial or an episode in a drama series?

So, already we have lots of metadata that may be incomplete, unreliable or ambiguous, and YouTube has to use that to figure out how all those videos relate to each other.

That's not the only thing YouTube uses, of course. There are other things: other videos you have watched, other videos you have commented on, liked or favourited, what kind of videos your subscribers watch, what kind of videos people you subscribe to watch, and so on and so forth ad infinitum.

At best, it's hit-and-miss.