There is a saying that people who really work hard can't feel how hard they work. For them, hard work is a natural thing, not as "terrible" as you think (this sentence is my own experience). Because truly self-disciplined people often have an extreme determination to accomplish something, they are very self-disciplined when doing the same thing. Self-discipline is terrible to you. In fact, self-discipline is really "effortless" for them.
The reason why you ask is because you don't have anything special in mind. You just want to work hard in this state itself, because "efforts are always right." And those who work hard, they just want to get things done. This kind of effort is a spontaneous state, just a by-product of achieving the goal.
I hope you can also be the kind of self-disciplined person in your heart.