Obsidian assumes your note names are unique
Obsidian makes some assumptions about the shape of your notes.
One of those assumptions is that the names of your notes (i.e. the basename of the file without the .md
extension) is unique across your vault, regardless of which folder it's in.
In fact, many people recommend using Obsidian without folders at all.
There is also a unique note core plugin that creates notes with a time stamp prefix.
I would say this is a "soft" assumption, meaning that you don't have to follow it, but Obsidian will be easier to use if you do.