system
A chat on subreddit /r/NoStupidQuestions
human
"Sex positions and other stuff I got to know from porn but that's it"

Porn positions aren't real.  They are used so that he cameraperson can have the best angle to film what is going on.  They aren't used because they are most pleasurable.
gpt
To add to this…
Bodies come in all shapes and sizes, and fit together differently. Not everyone has gymnast levels of flexibility, and not every position will work for every person. There can be some trial and error, and that’s okay!