In 1986, I watched William Shatner host Saturday Night Live. Great host, great episode: You had the Enterprise refitted as a theme restaurant and Shatner exhorting Star Trek fans at a convention to get a life, among other excellent sketches from one of the best casts in the show's history.
Behind the scenes, Shatner's performance impressed cast member Jon Lovitz. At SNL, Lovitz struggled with the pressure from writers and producers of the show to "be funny," week in and week out. "They would get you all riled up and tense every week," Lovitz recalled. Shatner, funny but not a comedian by trade, rolled in and made hosting—a job many agree is the show's toughest—look easy. So Lovitz asked Shatner how he did it. The actor, who had been working in theater, television, and film for over thirty years at that point, had a simple answer.
"Just do it," Shatner said. This was two years before the Nike slogan, mind you. This might be ironic coming from an actor who has never been known for subtlety, but Lovitz gave the advice a shot. He let go of trying to be funny (whatever that means) and focused on the mechanics of the job.
"I just said, well, what are they asking me to do?" Lovitz recalled. "I walk in a door, and then I stop behind a couch, and then I say something. So, walk and talk. I simplified it to that." David Mamet offers similar advice in his book on acting, True and False: Stop trying to achieve a certain effect or get the audience to behave in a certain way, i.e., laugh. Hit your mark, say the lines, and let the performance take care of itself.
"I did the show that way, without putting any stress on myself," Lovitz continued. "I thought for sure I wouldn't be funny, but after the show I thought, 'I wasn't less funny and I wasn't more funny. I was the same.'...What have I been putting myself through every week?"
This is equally true of writing. Why? You can't do the thing and try to do the thing simultaneously. It's too much. The simple act of writing is enough.
Yes, you should show up with a head full of ideas, but once you've decided on a specific idea, run with it. Surrender all your goals, intentions, and theories and focus on the mechanics of the job: putting down one word after another.
As mentioned, Robert Caro positions a note to remind himself of a key element as he drafts a given section. That's it! One reminder at a time. You can't juggle more than one overarching idea or conceit and still be present enough to do the writing itself properly. Worry about what you want the writing to achieve during the revision. For now, just do it.