For habits, there are only a few reasons to keep on something and a truckload of reasons to quit. All we can do is keep those few reasons nicely polished.
In Haruki's words:
"Running every day is a kind of lifeline for me, so I'm not going to lay off or quit just because I'm busy. If I used being busy as an excuse not to run, I'd never run again. I have only a few reasons to keep on running, and a truckload of them to quit. All I can do is keep those few reasons nicely polished."