Say you have a list of legally obtained movies on your hard drive. Hundreds of them piling up as your hoarding disorder worsen. You want to manage them somehow. So you start with a folder called "Scifi", and you put "Interstella.mp4" in there.
All things considered, Interstella is a scifi movie and it deserves the highest place in that particular folder. But you also love movies about a dytopian future, and the future of Earth depicted in that movie is no doubt darker than any DC movies to date.
Now you have finally realized the huge limitation of folders: A file can only have a parent folder. Interstella.mp4 can not be put in both Scifi and Dytopia. Period.
At this point, you should also have realized the superiority of tags over folders. This is the reason why I'm working on something called Tagthing. I built it for my own personal usage, with the following vision:
A challenge I see is that file paths can change, rendering the tag-data invalid. I have gather many approaches and will be trying them out in my free time.