Fighting, using the principles of Kung Fu, was best explained by the late great Bruce Lee when he said, "Kung Fu is like getting your Doctorate degree in combat from a University."
We are dealing with a paradox here, because the object of Kung Fu is never to have to resort to fighting in the first place.
But ...when you do choose to fight, you do so consciously. And you engage in combat completely. You destroy your opponent mentally, physically and spiritually. Actually, for the true practice Kung Fu fighting, the order should be mentally, spiritually... and hopefully, never physically.
How? You put your opponent into such a disadvantageous position that fighting is simply out of the question. In other words, you destroy your opponent mentally and spiritually, thus making it almost impossible for his physical body to react.
Here is an ancient Chinese story that demonstrates this point: One day a Kung Fu student was on his way to class when he saw his teacher fighting with another man on top of a huge boulder. His Kung Fu teacher reached out and touched his opponent with two fingers and the man fell to his death. The student ran to his teacher and said "Master, that was amazing! You killed a man with two fingers!" The teacher responded, "That was not the amazing part. The amazing part was convincing that fool to climb up on the boulder." Once the man had climbed on the boulder, he was destroyed mentally and spiritually; the rest was simply gravity and timing.
There's a catch, though. To practice Kung Fu fighting correctly, the student must be totally confident in his techniques. Only then can he choose consciously whether to employ them or not.