Put your feet shoulders width apart. Put you attention on the bubbling well point of each foot, and put your attention on the center of the heel of each foot; that's 4 points all together.
Now shift your weight from foot to foot while attempting to keep the pressure totally equal on all 4 points. It's a simple task but difficult to do. The more sensitive you are to fluctuations in pressure, the more you'll be aware of mistakes. After doing this for a few minutes, relax into feeling all 4 points as one distinct thing, one constant experience--as if all 4 points were in fact a single structure.*
In English, we tend to call this process "integration." It's like when you learn to juggle. At first you are trying to keep each ball in the air. Later, you just juggle. It's one thing. (Until you try to add a new trick.)
The exercise above is called 4 Becomes 1. Actually, we could call it "5," because the integrated state is a new thing. There are many "4 becomes 1" types of exercises.Â Sometimes they are labeled by the 5 Elements (Wuxing), wood, fire, metal, water--with earth being the fifth element.
4 Becomes 1, is not just an exercise, it is a principle of movement. Learning in martial arts is very often a process of taking several different ideas, feelings, or qualities of movement and making them a single thing.
This can be a great source of frustration for students if they don't understand the principle. As a teacher, I have in my mind 4 things I want to show you. I teach each of them to you as a distinct practice and then I try to get you to do them all together. Students, however, will try to cling to the one exercise they think they got "right." They want to get "good" at something. The teacher, however, doesn't want the student to do the four exercises separately. Getting good at just one would actually move the student away from the final goal. As soon as a student can do each of the 4 exercises at a basic level, I will try to get her to combine them.
Sometimes there aren't four distinct exercises to integrate. Sometimes four exercises will build on each other so that you learn one and then add to it. Doing the "one" plus something else, and then adding to it again, and then again. The result, however is supposed to be a simple singular activity-- composite perhaps, but also whole.
(Note: * The 4 in 1 exercise at the top is probably a really good exercise for golfers.)