"Most of what I know about writing I've learned through running every day. These are practical, physical lessons. How much can I push myself? How much rest is appropriate - and how much is too much? How far can I take something and still keep it decent and consistent? ... How much should I be aware of the world outside, and how much should I focus on my inner world? To what extent should I be confident in my abilities, and when should I start doubting myself?"
Haruki Murakami, What I Talk About When I Talk About Running, p81-82