Why can't static variables be operated in static methods? What should I do?

Why can't static variables be operated in static methods? Why can't static variables be operated in static methods? For more information, see <g id = "1">. </g>. This object is generated at runtime. Generally, non-static methods can operate static methods and variables. Static methods cannot operate non-static methods or change static methods. why cannot they operate static variables?
Why can't static variables be operated in static methods? Explain ..

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Static methods are defined during compilation, and an object is required to operate non-static variables. This object is generated at runtime.
Generally, non-static methods can operate static methods and variables. Static methods cannot operate non-static methods and variables. (However, php can call non-static methods statically in violation of regulations)
Http://cn.php.net/manual/zh/language.oop5.static.php
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It doesn't matter if I make a mistake, as long as you don't become stupid.