You can't focus on "writing" if your keyboard keeps sticking or some key doesn't work. Your attention leaks out from word/sentence level to letter level. Generalizing, to work at level n, you need to be able to trust level n-1 at unconscious level.
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That point is obvious. It's less obvious that you also need to be able to trust level n+1 above you. You can't write if you can't trust your situation awareness of the zeitgeist at the time constant of your writing (minutes for tweets, days/weeks for blog post, years for books)
