The great chi Kung master Obi-Wan Kenobi said it best.
Your eyes can deceive you. Don’t trust them.
Today I closed my eyes as I worked through the form in the sunshine. It’s elegant. When your eyes are open, your dynamic sense of balance tells you that your body is stable and in balance. It isn’t. Your feet are working hard to keep your balance, but your head gets none of that data, or only a little bit.
The first time I did the form with my eyes closed, I was stumbling and falling all over the place. My eyes had been deceiving me. But the inner ears are not capable of that kind of deception. They cannot tell you that you are in stable, gravity-dependent balance when you are actually in dynamic, muscle-dependent balance. One cannot be replaced with the other, without noticing.