Diffusion; it is a natural effect. At least on earth, as far as I know, emptiness is always filled. By liquid, by gas, by air. A natural movement of particles is always on the move to find a new equilibrium. It is in constant move.
This natural effect can also be observed between people and their interactions. Example: if a person is passive and has a character that tends to evaporate a fellow human being will fill the gap. It is beautiful to observe, it can go back and forth and vary in time and place between all the individuals that are tied by this effect.
Human reactions are like gas. The definition of gas is: an airlike fluid substance which expands freely to fill any space available irrespective of its quantity. The question is: does it expand freely or is it a law of nature? Are humans acting or reacting. How free are they? Aren't their actions not, most of the time a natural effect within a much bigger space called Universe? And is it not a fact that they have very little influence on their choices and the constant movement?