The word 在于 is formed through the combination of two ancient, core characters, each contributing a fundamental spatial-relational concept. 在 conveys the idea of "presence at" or "existing within" a specific point, while 于 functions as a classical preposition linking that point to a broader scope or basis. Their fusion creates a single, abstract verbal unit that conceptually frames the essence or cause of something as being intrinsically located within, and thus determined by, another stated condition or principle.