Another thing to keep in mind if you think you’re running too slowly for it to be worthwhile: Your basic aerobic fitness is the main determinant of how fast or slow feels comfortable on a typical daily run. The fitter you are, the faster will feel comfortable. And for almost everyone reading this book, the best way to advance that fitness is to run more, rather than your normal amount at a faster pace. As you get fitter through more mileage, what feels like a comfortable everyday pace will eventually become faster. By slowing a bit now while building your mileage, later you’ll be running more, and at a faster pace, than might seem conceivable now.