The irreversibility of the macroscopic world.
Known generally as Epicurus' clinamen, it decribes the minimum declination from a flow of particles that would give birth to vortices.
Used as an early explanation for the emergence of the material world, and life, through increasing complexity, and chaos, it could be summed up as:
I like to think of it, in some strange way, as meaning:
The exception that proves the rule