In photography, the foreground is the key, three points and nine squares. What does this sentence mean and how to use it?

The so-called three-point nine-square grid, also known as the fun center, is psychologically divided. According to scientific experiments, people who stare at the painting center for a long time will have visual fatigue, which leads to another series of outstanding themes. If the picture is regarded as a bounded area, the left, right, up and down are divided into three equal parts, and then these corresponding points are connected by straight lines to form a tic-tac-toe in the picture, and the picture area is divided into nine equal squares, which are called "nine squares". The four intersections of tic-tac-toe are the interesting centers. This is the long-standing composition method of "Jiugongge" in our country.

Putting the subject near the center of interest is the most commonly used method. The subject is not only prominent but also flexible in this range, unlike the geometric center, which lacks change. The fun center is shown in the following figure: