So the intuitive idea that you start with a burst of motivation and then you maintain it with discipline is wrong. Motivation is exactly the kind of impulsive distraction that destroys discipline.
Starting with discipline means rejecting random motivation when it comes, just like you might want to reject candy or lighting up a joint. Starting with discipline means you make the commitment first, and you fight to stick to it without any of the motivational high.
From that lens, I started seeing "get my life together" thoughts at 1am to be as bad as the worst impulses I struggle with.