[because people are like atoms: you shouldn't cut them into pieces. (just kidding, that's not my rationale)]
In chemistry, there's the notion of resonance structures. The Lewis dot diagram can't actually capture a molecule's spirit, because it simplifies too much: flattens, and makes arbitrary decisions about where to put the double bond that has to take up the wandering orphan electron. Sometimes there are two or three equally good (and equally inadequate) dot diagrams of a molecule, and the molecule is said to "resonate" between those structures, because while no single one of them expresses the molecule alone, the real molecule is somewhere between all of them--not quite a sum, not quite an average.
"Resonance" arises as an artifact of having to diagram in two dimensions what lives in three dimensions; it isn't a real phenomenon in the sense that the molecule doesn't actually alternate between those structures. However, the concept that underlies it is real: that realities transcend all representations of them.
And your point is? you may be asking.
My point originated in a comment from my friend O. about being most comfortable switching at will between orthogonal tones (my phrasing, not to be blamed on O.)--from silly to serious, from flippant to enigmatic--which sparked the thought that those spontaneous switches of tone are the thing that characterize a really comfortable relationship.
See, we all have a collection of faces we can present. Reliable, intelligent, well-behaved, adventuresome, empathetic, aloof: A person who embodied one of those characteristic faces could not also wear any of the others. Like the distinct diagrams of resonance structures, they are mutually incompatible. Moreover, no single trait adequately describes a person, just as no single resonance structure accurately describes the behavior of a molecule. Like molecules, our personalities are multidimensional. Our different faces appear and disappear in the context of interactions with other people--the souls we're bonded to, the spirits we're close to.
Moreover, a real relationship has many dimensions to it. You don't just talk about class, you also talk about philosophies. You don't just talk about abstract ideas, you talk about realtime emotions. You don't just know what the other person thinks about the deep structure of life, you know about their day to day experience. All those domains flow into each other, like trees with intertwining branches, not like rooms in a house. You alternate between topics in the verbal representation of your bond (i.e., the conversation), but underlying all the words that code for concepts is the understanding that every layer of meaning is present at the same time. When my friend starts talking about the spiritual significance of Jesus's solitude, I don't assume the idea sprung into existence on its own like Athena sprouting full-grown from Zeus's head. I know there's a good chance that some emotional experience fertilized the blossoming ideas; I know the meaning my friend conveys isn't all in the words or even in the topic. It's embedded in the relationship, in the bond.
And how would I characterize that bond between good friends? It spans the levels of understanding, it resonates between them. Catch the spiritual implications of the mundane, and the concrete implications of the abstract: the conversation doesn't alternate between them as though between discrete states, but rather has all of them present at the same time, because they are all aspects of the relationship. With a friend, I am more fully myself, because together we each resonate through our whole self. And with a friend, I am more than myself, because we each resonate through each other's self. A friendship and a soul, both are more than the sum of their parts.
A relationship is about understanding, having one mind, shared thoughts and energy. It's about functioning together, as a unit. Alone we are atoms; by caring about each other, we join ourselves together into complex structures. These molecules are dynamic, shimmering; they are real, and they transcend the descriptions by which we attempt to portray them.