When two (or more) systems are in interaction, each system has its own level of complexity, which is usually tied up with how many degrees of freedom the system has for taking independent actions at a given time. Since these levels of complexity are almost never the same, there is a complexity “gap” between the systems taken pair wise. If this gap becomes too great, the stress between the systems starts to enter the danger zone. This is much like stretching a rubber band to its limit of elasticity. If the gap is not narrowed voluntarily by the systems involved, human nature steps-in to forcibly narrow it by creating a crash, an X-event.