Mushin

Takuan Soho, the famous Japanese Zen master describes mushin this way in his book, "The Unfettered Mind" :

"The mind must always be in the state of 'flowing,' for when it stops anywhere that means the flow is interrupted and it is this interruption that is injurious to the well-being of the mind. In the case of the swordsman, it means death. When the swordsman stands against his opponent, he is not to think of the opponent, nor of himself, nor of his enemy's sword movements. He just stands there with his sword which, forgetful of all technique, is ready only to follow the dictates of the subconscious. The man has effaced himself as the wielder of the sword. When he strikes, it is not the man but the sword in the hand of the man's subconscious that strikes."

Ego chains (or "fetters" in Takuan-san's words) the mind when faced with an enemy. Ego desires self-preservation and thus is the root of fear. Fear stops the natural flow of the mind and impedes the actions that result from that natural flow. In extreme situations, this can result in a paralysis of fear and ultimately can result in death under some circumstances. A more benign example is "stage fright". Some people become paralyzed with fear when they have to speak in front of a crowd. Why is that? Because they are afraid of being negatively judged and critiqued by fellow human beings. The exact same thing can happen in combat or under any kid of stress. Very few of us can rise to the occasion. Most of us fall to our level of training when faced with a stressful situation. In Aikido, we look to raise our level of training so we do not fall as far.

Ego drives and is the root of this paralyzing fear. Eliminate the ego and the fear is gone. This is done through cultivating mushin everyday.