请问中括号里的that引导的结果状语从句修饰哪个词?

请问中括号里的that引导的结果状语从句修饰哪个词?
完整句子：That most working people do not go mad is due to a phenomenon so common [ that it is found wherever people labor in industry ].
中括号里的that引导的结果状语从句修饰哪个词?
so common that that引导结果状语从句，句中的it是指前边的 a phenomenon
He got up so early that he caught the first bus.
【结果状语从句】：
常用引导词：so … that,such … that,
特殊引导词：such that,to the degree that,to the extent that,to such a degree that,
He got up so early that he caught the first bus.
他很早起床以便赶上第一班公共汽车