I understand this in the context of improvisation on the piano. If it's just intelligence, I understand which chords work with which scales (keys). I know strategies on how to play chords in different ways, how to play bass notes with the left hand while playing chords with the right, and how to play random notes from the scale with the right hand while playing chords with the left.
If my fingers can't do what my brain is imagining, I can't create new melodies. There is no mastery. When it comes to "writing every day", I don't think writing anything just for the sake of writing is what that advice is about. A seven-year-old can "write every day", but that alone isn't going to grow his skill. There has to be more to it than that, but I don't know what that would look like. With music, I know what to practice to get my fingers to behave as I want them to.
I enjoy learning new things in quite a few different subject areas, but I don't know how to join them together. I don't let my mind just wander nearly enough since I'm always listening to something. I'm stuffing myself with "input". I guess this makes me an intellectual "glutton".