The Marathoner’s Guide to Accomplishing Anything

If you want to run a marathon successfully without getting injured, spend four days a week doing short runs, one day a week running long and hard, and two days a week not running at all.

Now, that seems like a pretty smart schedule to me if you want to do anything challenging and sustain it over a long period of time. A few moderate days, one hard day, and a day or two of complete rest.

— Peter Bregman, 18 Minutes: Find Your Focus, Master Distraction, and Get the Right Things Done