Newton's third law
The mutual forces of action and reaction between two bodies are equal, opposite and collinear.
When you string a racket on a two point stringer the two points support the racket from bending inward. Many inexpensive two point machine do not hold well.
When you string a racket on a six point stringer the two points at the top and bottom support the racket from bending inward. As the frame tries to bend inwards from the top and bottom the sides try to bend outward. The four supports on the sides of a six point support the racket from bending outward and help prevent the frame from bending inward from the top and bottom.
If your racket is shorter it is wider too or more circular. This causes the racket to be under stress while you are playing with it because the strings are what is keeping the racket deformed. Therefore, there is more tension on your main strings that you have on the crosses because the frame is trying to return back to it normal state.
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