The concept of "Mushin" can best be defined as being "in the zone." Its when an individual enters a warrior state of mind in which there is literally "no mind." He or she doesn't think, over analyze, or even fully comprehend in real time what is taking place other than they are performing at their highest level.
A Buddhist warrior concept, Mu-Shin's Kanji is derived from the following characters:
Mu - which means "negation" (left)
Shin - which means "heart, spirit, feeling" and or "mind" (right)
Ever driven to a destination, arrived, but then suddenly start wondering how you even got there? You drove safely, you obeyed all traffic laws, yet, couldn't for the life of you recall ever putting deliberate thought into the many actions that got you to your destination safely? That's a bit of a crude but great example of the feeling of this mental state. No doubt you've driven quite a bit over the years and maybe to the same destination a multitude of times such that your body and mind know where to go, what to do, and how to get there. But still, you may wonder how?
Better yet, ever played in a sports game and had one of the best games of your life? Throughout the game, you accomplished feats of greatness that came so naturally, you're not 100% sure how you pulled them off. Yet, you did. You did not take any performance-enhancing drugs, or cheat, yet, you just felt "on," and when friends and teammates ask you what happened, you can simply answer with something similar to that hilarious Will Ferrel quote: "what happened I blacked out?" from Old School?
That's the essence of Mushin.
Mushin is achieved through the results of many hours, days, and years of mental and physical practice. Of putting the body through the rigors of training such that it understands the basic mechanics of an action and can move onto other things. Its when the brain is able to take a backseat and performs without overthinking and hyper-analyzing every action. You see the attack coming because you feel it, because your senses are so aware, that your body postured to receive the attack is doing so and reacting naturally.
One of the greatest examples of Mushin comes from The Last Samurai. Now, mind Tom Cruise and say what you will about the movie, but this clip is a perfect set up:
Cpt. Nate Algren (or Tom Cruise) is attempting to learn how to fight with the Katana sword via Kenjutsu Training and is spending too much of his mental focus on the people around him, how he looks, his frustrations, and everything but the only thing that matters: his opponent in front of him.
After a quick tip from one of the younger Samurai warriors, he is told to stop minding the people and everything else, and that he has "too many mind."
After getting knocked down a few more times, it seems like he finally begins to understand what he is doing wrong and applies this concept during his training with one of the village's best warriors:
This results in a draw, taking Cpt Algren from a bumbling, uncoordinated mess to a composed warrior adapting to another method of combat. The scene overall really helps solidify the concept behind "too many mind" and what happens when Mushin is practiced.
Compounding off the previous examples, later on in the movie, Cpt. Algren is attacked in the streets by three armed men. Weaponless, Cpt. Algren relies on his training to take on the attackers. As he does so, he seemingly, "goes with the flow," seizing opportunity after opportunity to gain the upper hand and ends up killing the three assailants and mentally replays would just happened.
As he stares mindlessly into nothing and mentally replays what the f just happened (it's all over his facial expression), it's evident his training in Kenjutsu took over. He didn't worry about not having a gun, or how unfair the odds were. He wasn't consumed with how his technique was, or that the attackers didn't attack "the right way." He simply reacted. He took the teaching and training that was provided to him and he executed.
This is Mushin.
It would seem with many Buddhist and martial arts based concepts, that defining that which literally has "no mind" as one of its prevailing definitions would be difficult, and it is. However, the concept and practice of Mushin is such a rewarding and beneficial outlook on life that there will be many more entries explaining this and how it can become an achievable everyday practice.