Digital Media Concepts/YouTube's Algorithm
The algorithm of youtube is a touchy subject but is connected to three things. The monetization of youtube, suggestion, and the view counts per video. By watching a video that video will gain a view just by clicking on the video. But by how much time you watch the video that will go into monetization, the views per minute will then slowly seep to trending. And by watching or any activity on youtube will then later be suggested to you.
Not much is known due to google keeping the history of the algorithm and YouTube under lock and key.
Suggested Videos edit
Now they suggest videos by common searches you watch. for instance, if you watch a lot of scary top 10 videos the they will start recommending you that until you say not interested then they will stop. this on the other hand does fall through due to over complications on googles side of things. you can see this when you watch anything that includes a tag on it. this can be seen when you post a video and insert tags or even in the description.
The trending tab is connected and can be predictable such as news and artist. But sometimes will upload popular videos and show them and the tab is updated every 15 minutes and each country has their own tab depending on the country too. Not much is known but it can be seen that videos that are trending due to them having high views.
There are loopholes? Yes there is but its really easy to get around it and it is by using a few things such as easy things like click bait either titles, thumbnails, or both. There is a higher chance that you will click on a click bait title over a title that is good/informative. Another way people do get around the algorithm so people watch their content is by re-uploading videos that they have created.