That's it, and that is constantly it. Again, nothing else is thinkable. When athletes practice or coaches run a practice without trying to improve, they are just fooling around. That doesn't mean that all practices have to be hard. Coaches and athletes live in a world which teaches, respects, honors, demands and rewards hard work.
Hard work is the way athletic achievement is accomplished.
As it is in the martial arts, where the saying is that the Master is the one who spends ten more minutes on the mat, so it is in all of athletics. Hard work is essential for continued and lasting success. All of trifling, and all of fitness are built on the principles of work-rest, and progressive overload. The way to improve from one level of fitness to the next is by working harder. There is no substitute.