I've taken up running in recent years, and it's done me quite a lot of good. Besides feeling better physically, I have benefitted from knowing that I, an old dog, am still capable of learning new tricks. I'm not a natural runner; cultivating the discipline to do it has taught me lessons that have applied elsewhere in life, including my writing life. Here's the most important thing I've learned from running: when I find myself miles from home and exhausted already, I've learned not to ask, "Can I run all the way home?" The truth is, I usually don't know whether I can run all the way home. I have learned instead to ask, "Can I run to the next light pole?" The answer to that question is almost always "Yes." And once I've made it to the light pole, I start thinking about the next light pole.
Of the few books I've read about how to write, my favorite by far is Anne Lamott's Bird by Bird. That book has done much to shape my day-to-day approach to writing. Lamott compares writing a book to driving at night. Your headlights don't illuminate any farther than the next turning. But you keep going anyway, knowing that by the time you make that turn, your headlights will light the way to the next turn. And eventually you get where you set out to go.
Writing a book is a daunting task. Writing, like night-driving or distance running, requires a certain amount of faith. You set out for a destination without knowing exactly how you're going to get there. For me, at least, it helps to remember that I don't write books. I write sentences. A book is what you have after the fact. On any given day, I'm only writing pages. I'm only running to the next light pole.