Perhaps the most significant thing is that I write even if I feel the words will sound like a third grader. When I was a college student, I had deadlines for my papers and I was never late.
One of my close friends in grad school never once turned in an assignment on time. His grades were always reduced, and he'd say, "If I had had more time, I could have done a better job." We call that rationalization. He had as much time as the rest of us.
When I taught public school for two years, I couldn't say, "I didn't feel motivated to prepare a good lesson plan this week." I just did it. Some weekly plans worked better than others, but I did what my job required.
Professionals write and meet deadlines. Regardless.