There are certain skills common to all good fighters that make their art effective. The reader should not become confused between a good fighter and a successful fighter. I would argue that all it takes to be a successful fighter is to be a breathing human being, because the only substantial criteria demarcating success as a fighter is survival. Good fighters, on the other hand, generally adhere to three fundamental principles.
To defeat an attack a good fighter will yield, merge, and issue force, in that order. To yield is to respond to an attack. A fighter may yield by dodging, darting, twisting, ducking. An experienced fighter knows that it is pointless to survive the first attack if all you have to look forward to is a second one. Therefore he will attempt to yield in a manner that will set him up to merge with his opponent. To merge is to develop a connection. This could consist of coordinating his position and movement with that of the opponent or making physical contact. If the fighter merges effectively he is able to issue his force in the desired manner into his opponent’s body. The force could be issued in a variety of ways such as a push, a penetrating blow, or a whipping strike.
A good fighter issues force from an inherently stable posture. An inherently stable posture is a position in which the body is able to stand freely on a well-aligned skeleton that supports the majority of its weight so that a minimum amount of muscular exertion is necessary. Standing with such a posture feels effortless and without strain or tension, which makes it easy to respond readily to any force that may be exerted on the body. For any such force of reasonable magnitude, it is possible to assume a position where the muscles of the leg can effectively exert a counter force without becoming unbalanced or experiencing undue strain in any part of the body. This is an inherently stable structure. Positioning yourself in such a way you will feel to your opponent like a rock stuck between him and the ground. Lacking such alignment means you will be more vulnerable to harm and your movements will feel more difficult to you and weaker to your opponent.
A good fighter generates force by pressing against the ground and moving the body as a unit, issuing force in the most efficient manner possible. All movement of the body from a standing position is a result of the feet pushing against the ground. The ground is acted upon by a foot, which is acted upon by a leg, which is acted upon by the large muscles of the thigh. If the kinetic energy is able to travel unopposed through the body then the force that the foot exerts on the floor will be transmitted through the waist to the shoulders and go on to express itself through the arms and hands. But it is the same force. Kinetic energy is transmitted most readily through relaxed muscles supported by an inherently stable structure. A relaxed but confident fighter is generally considered to be very dangerous. He generally is. (For a mental image, picture Brad Pitt in Snatch, or Tom Cruise in Collateral.)
These three principles are interconnected, and a fighter’s likely effectiveness is based on how easily he or she applies all three of them (though we shouldn’t forget that a fighter may be able to win many fights through sheer luck, or by applying the principles incompletely). You can yield, merge, and issue force most efficiently from an inherently stable structure while moving from the heels. Your posture cannot remain inherently stable if you are not able to yield effectively to an external force and move your body optimally. All your efforts to issue force will be in vain if your structure is flawed or you have not developed a firm connection with your opponent by yielding and merging. The principles of fighting are not separable; the effectiveness of each depends on the others.
Finally, note that any altercation involves an element of chance. You cannot attempt to harm someone without putting yourself at risk. It is always best to be willing to accept losing what you risk, whether it be a fingernail or your life. Not only will your soul be more at peace, your kung fu will work better.