Right effort refers to how you pay attention. You cultivate and train your mind in order to shift your attention from one object or thought pattern to another. You learn how to apply effort in this manner so that when you find yourself obsessing on a thought that is not wholesome, you have the ability to shift away from it. Such a shift comes from your wise understanding and right intention, not from aversion. When your mind is focused in a wholesome manner, you have the ability to sustain your attention.