The way I’ve heard it, your “reward” is a closer relationship to Hashem. In this respect, it is like how one may not always want to do things for one’s wife and children, which may feel like drudgery at time. Even so, one gives and does anyway out of commitment to deepen one’s relationship.
Some days the brain and action is driving the mitzvot. Other days it’s the heart.
At least that’s how it was explained to me.