It's about finding the right balance needed for a particular situation. If you need a little more energy you can think "attack" in your mind. Or if you're getting bit overaggressive, angry, frustrated, or out of control, think "smooth".
It's somewhat similar to when Bruce Lee speaks of being calm but alert in the Tao of Jeet Kune Do:
“Not being tense but ready. Not thinking but not dreaming. Not being set but flexible. Liberation from the uneasy sense of confinement. It is being wholly and quietly alive, aware and alert, ready for whatever may come.”