GTD (Getting Things Done) is a unifying workflow for all tasks. It works well by treating the job holistically.
It does not make completing tasks easier, but when you write all your tasks down, you do not worry about them anymore, you free your mind and are able to concentrate on the task at hand. (And have easy mind in general.) (Zeigarnik effect)
In a similar way, § Zettelkasten allows your mind to think freely. It approaches the learning–note-taking–papers-writing workflow holistically and makes frees your mind from remembering all the ideas and makes connecting and looking through them easier so you have a piece of mind.
In that sense, § Zettelkasten is GTD of note-taking (learning?).
- Zeigarnik effect explains why this happen—by writing down tasks/notes, we literally free our brain from them.