Mathematician Paul Halmos, from the Notices of the American Mathematical Society:

I love to do research, I want to do research, I have to do research, and I hate to sit down and begin to do research—I always try to put it off just as long as I can. It is important to me to have something big and external, not inside myself, that I can devote my life to. Gauss and Goya and Shakespeare and Paganini are excellent, their excellence gives me pleasure, and I admire and envy them. They were also dedicated human beings. Excellence is for the few but dedication is something everybody can have—and should have—and without it life is not worth living.

Despite my great emotional involvement in work, I just hate to start doing it; it’s a battle and a wrench every time. Isn’t there something I can (must?) do first? Shouldn’t I sharpen my pencils, perhaps? In fact I never use pencils, but pencil sharpening has / become the code phrase for anything that helps to postpone the pain of concentrated creative attention. It stands for reference searching in the library, systematizing old notes, or even preparing tomorrow’s class lecture, with the excuse that once those things are out of the way I’ll really be able to concentrate without interruption.

He also has this fascinating bit about how many hours of sustained attention he is able to maintain. It matches up pretty exactly with… almost everyone else I’ve looked at.

During my productive years I probably averaged 20 hours of concentrated mathematical thinking a week, but much more than that was extremely rare. The rare exception came, two or three times in my life, when long ladders of thought were approaching their climax. Even though I never was dean of a graduate school, I seemed to have psychic energy for only three or four hours of work, “real work”, each day; the rest of the time I wrote, taught, reviewed, conferred, refereed, lectured, edited, traveled, and generally sharpened pencils all the ways I could think of.

Halmos was also in the habit of walking a lot every day, and was “one of the discipline’s most enthusiastic and vigorous practitioners.” In his 70s he was affiliated with the math department at Santa Clara University, and according to one of his collaborators,

the way to ensure one’s getting the minimum daily dose of one hour (equals four miles) is to live two miles from the office. Paul claims (and there’s no reason for doubt) that he found the San Jose house by drawing a (Euclidian) circle of radius two miles, centered at O’Connor Hall and scouting the perimeter.

Indeed, there’s a Halmos commemorative walk in Washington DC.