đź“ťThe principle of GTD is getting things off of your mind
The main principle of GTD is getting things off of your mind. This way, you stop ruminating the same idea in your head and you are free to use your mind for other creative purposes.
See also
Zeigarnik effect—the psychological effect behind this.
Zettelkasten is GTD of note-taking—Zettelkasten (or any note-taking) tries to achieve the same effect w.r.t. ideas.