The word 彼此 is formed through the complementary pairing of two distinct demonstrative characters: 彼, which originally pointed to something distant or "that" (the other), and 此, which pointed to something near or "this" (the self). Their combination does not create a simple list, but rather a conceptual whole representing a reciprocal relationship, directly encapsulating the idea of "each other" by inherently referencing both sides of a relationship, the one here and the one there. It is a classical Chinese construct where two opposites merge to express a single, unified concept of mutual reference.