Motivation is a mood. Discipline is a structure. Moods come and go; structures hold. This is the entire argument and the rest of this article is just elaboration.
The waiting trap
Most people who want to change something — fitness, faith, writing, finances — wait to feel like doing it. They are waiting for an internal weather system to cooperate. The weather rarely cooperates.
Discipline says: I have decided in advance what I will do today, and I will do it whether I feel like it or not. This sounds joyless. In practice it is the opposite of joyless. It frees you from the exhausting daily negotiation with yourself.
What scripture says
"No discipline seems pleasant at the time, but painful. Later on, however, it produces a harvest of righteousness and peace for those who have been trained by it."
— Hebrews 12:11
What philosophy says
"We suffer more often in imagination than in reality."
— Seneca
A small experiment
Pick one thing — one — that you keep wishing you did. Make it absurdly small. Do it at the same time every day for two weeks. Do not let yourself negotiate. At the end of two weeks, notice what happens to your sense of yourself.
Discipline is not the enemy of joy. It is the road to it.