I was meeting with a member of my doctoral dissertation committee. We were reviewing a draft of the opening chapter of my dissertation. As the office door was open, in sauntered a fellow doctoral student who also was working with this same faculty member.
The student stated, "Dr. Jones (not her real name), I'd like to talk to you about my dissertation proposal." Dr. Jones looked at the student somewhat quizzically, paused, and replied with all due enthusiasm: "Talk about it? There's nothing to talk about. You haven't written anything. When you've written something send it to me. Then we can talk about it."
That comment by itself reinforced for me the urgency of writing. That means not just thinking about writing. Nor does it mean merely talking about writing. It refers to actually writing about your proposed topic. There is no substitute for doing so.