Willpower is a limited resource, so use less of it by making challenging activities automatic. By setting a time for your routine, you don't have to spend energy thinking about when to get it done. If you find yourself faltering, reduce the challenge but stay the course. Run three days a week instead of four. Repetition, even in very small doses, builds capacity. Any positive change you can make will be hugely satisfying — and a source of inspiration to make the next one.