Our world is an illusion. A fantasy that was destined to end when we were first borned. Some people just happened to make it last a little bit longer than others. The inevitable fact being that all of us will turn into ash one day, whether we like it or not.
Scientifically speaking, the body is an illusion because of its fundamental making up. To dissect every individual cell of our body will finally find that they are but constituents of electrons, protons, neutrons, and etc. And they are capable of emitting energy. Or changing their forms into energy following the law, E= mc2.
Hence our body is capable of becoming energy, which is our mind. That is why we have body and we have mind.
However not every being has a manifestation of mind. For example, a piece of rock. But they have the 'potential' to have a mind. It is in the state of potential energy.
It is true to say that mind and body are inseparable. A confused mind would lead to discoursed body movement. The trouble is we really have problem to control our mind. Take our heart beating,or dreams for example. If only we can control our dreams. A confused dream is a sure sign of a confused mind. Hence in difficulty to control our body. If we cannot control our body, we would have difficulty to control the opponent's body with 100% confidence.
Therefore it becomes the ultimate challenge of a martial artist, to become the master of our mind.