We talked about "mushin" so why not talk about "shishin".
"Shishin" is written in kanji (Japanese version of Chinese characters) as "Stopped Mind".
It means your mind stops at one place.
In other words, you are worrying about or concentrate on one thing and cannot pay attention to anything else.
Doesn't it sound familiar?
Yup. You heard the same kind of stuff in the article about "mushin".
As explained, you do not want your mind stay at the one place. Your mind should keep its flow.
Have you heard a story about the water by Bruce Lee? You can see it here.
He talks about the quality of the water. The water can be so strong so it can destroy a rock. The water is so soft that it can change its shape into anything depending on a shape of a container into which it is pored.
One thing I want to add is that even the water gets rotten, if it does not flow.
If it stays at one place for a long time, it will be rotten. It will be dirty. It will lose its clearness. It needs to flow. You mind as well has to flow.
I am sure you have an experience that you are totally stuck with, say a math problem.
You cannot solve this math problem. The more you think, the more you get stuck. You come up with the same solution over and over and you get sick of it.
However, if you do it next day, you can solve the problem easily.
Your mind was stuck with one way to solve the problem. You could not think any other ways to solve it because your mind was stuck.
Once it gets it's flow back, you can come up with solution that you could not think of the previous day.
Let it flow, mate. Let it flow...