When your hand is trying to move the balls on your palm, its proficiency can be divided into four levels.

Level 1: Your hand is trying to move the balls, so it is not so smooth.

level 2: The fingers seem to follow the movement of the balls. Slightly smoother.

Level 3: Feeling of unity, as if your hands are controlling the balls and the balls are controlling the hand at the same time. And as if 2 balls are getting together. Yin is Yang, also Yang is Yin. It is like superposition

Level 4: The Balls are moving more smoother, your hand looses the sensation of what the balls are on your palm. The balls as an object disappears and the hand as a subject also disappears. Or the balls can be a subject and the hand can be an object. It doesn’t matter which.

Neither what your hand is controlling the balls nor what the balls are controlling your hand. Nothing is existing, just energy is flowing. This is the truth through the point of view of Zen Buddhism.

 In the same way, Zen perspective can also explain whether the chicken comes first or the egg comes first. Neither comes first or second, nothing is existing, only energy flows. In the same way, it could explain where you were before you were born and where you will go after you die.

 Meditation can be similarly divided into 4 levels.
The last stage is the state of “Ku” 空 as referred to in Zen Buddhism.