Yes, I can sit still for hours, noodling over some nuance, re-reading the paragraph I just wrote more times than is necessary, looking up an arcane fact I could live without. But the rabbit holes are tempting and I finally have time to explore them. All of which is to say that I can sit still and write (or pretend to) for the entire day.
And so ... thank God for deadlines. I've lived with them since I was in grammar school and had to write book reports and term papers, worked as a magazine writer and editor where they were so much a part of the furniture that I hardly gave them a second thought. Now I have deadlines to submit analytical essays and research papers.
Of course, I deplore deadlines. I rail against them. But without them the learning — and the sitting — would be eternal. And we can't have that.