I say, "Cecil, sit down and f--n write."
Sometimes, you write what you needed most to write. And what you thought you should write, if it's to be, will come in time. If you take on commercial deadlines, surprise yourself by NOT putting it off, just catch yourself in an unguarded moment when you were going to entertain yourself with, essentially, a distraction. Start early, so you can work to your heart's content. You may need deadline pressure to finish it, but Blank Page drama is avoided. And sometimes, it'll happen anyway, because it's what you needed to achieve a real breakthrough with after effects in your entire creative body. So don't waste time beating yourself up when this happens.
That's Rule #1, anyway: Be Good To Yourself. Meditate. Do something physical that will make you present in your body, in the moment. Spend time with your pet. You're not there to be your own slave; you're there to FREE yourself.
Photo: TW Hank
Sometimes that means "letting" yourself do your work. But if you can't write, do something worthwhile with the time. That's key. Then your sense of well being will be preserved, and your writing will be an extension of your sense of purpose, which you've just used to keep the foundation of your life around writing stable. Give of yourself to someone who could really use your help, and you'll see your writing continuing that intention. Sometimes, one can't write because some other thing really merits immediate priority. This is part of us being human beings first, which then write.