The feet must always be directly under the body. Any movement of the feet which tends to unbalance the body must be eliminated. The on-guard position is one perfect body balance and should always be maintained, especially as regards the feet. Wide steps or leg movements which require a constant shift of weight from one leg to the other cannot be used. During this shift of weight, there is a moment when balance is precarious and so renders attack or defense ineffective. Also, the opponent can time your shifting for his attack – Bruce Lee, “ Tao of Jeet Kune Do”