We may think there is willpower involved, but more likely... change is due to want power. Wanting the new addiction more than the old one. Wanting the new me in preference to the person I am now.
Success means having the courage, the determination, and the will to become the person you believe you were meant to be.
Exercise is done against one's wishes and maintained only because the alternative is worse.
Happiness is different from pleasure. Happiness has something to do with struggling and enduring and accomplishing.