Whenever you enter a dojo or a Japanese person's home we are kindly asked to leave our shoes in the genkan or front entrance way. From a practical standpoint, we are being asked not to bring in the dirt from the outside. From a dojo standpoint, we are being asked to leave the outside world at the door. This simple act is actually a martial arts training metaphor - don't bring the outside inside. The teaching we are trying to actualize is creating this calm demeanor inside that is not disturbed by anything from the outside. Nothing should disturb us when we are confronted by an opponent.
To not let anything outside of us affect the inside of us is very difficult to achieve. In Buddhism, it is called equanimity and in swordsmanship it is called the non-abiding mind. A dojo is place where we get to go and work on our equanimity and thus the environment needs to be free of outside distractions. Furuya Sensei used to say, "Cut off your head and leave it outside the door."
In the beginning we try and leave the outside world outside, but later as we improve we try and manifest what we learned in the dojo in the outside world. If we can do that then we can get to a place in our lives where we don't need to "react" and thus can act appropriately to the situation. If one can get to a point where they can observe their opponent and not react then you will have taken the first step toward what the Buddhists call mushin or no-mind which is one of the highest states of consciousness in not only Buddhism, but in the martial arts too.
To travel toward a state of mushin, begin by leaving the outside world and all its problems and stresses outside. As Sensei used to say, "Only bring what is good from the outside into the dojo and then only take what is good inside the dojo and apply it to your life outside of the dojo." This is how studying the martial arts makes you a better person.
Becoming a better martial artist begins with taking off our shoes before we enter the dojo leaving the outside world outside. Please don't let the outside affect your inside.