Chaos Control is the act of manipulating something that, by all other known logic, shouldn't be possible to manipulate. All acts that don't have any logical explanation, including spontaneous super powers, the paranormal and universal energy sources, all have roots in the act of Chaos Control to some degree, and consequently, the very element of Chaos itself. Chaos in of itself is an element that by nature cannot be controlled, as it stands for the exact opposite of control and behaves however it feels like behaving - however, through the act of controlling Chaos, one performs an impossible action. Random chance is no longer random, laws of physics and nature no longer apply, and reality itself bends to the will of the wielder. Chaos Control is an oxymoron in that it implies the ability to control the uncontrollable - once that is possible, the wielder technically has the ability to do anything they believe they are capable of, regardless of whether explainable theorem suggests they shouldn't be able to.
While Chaos Control can allow virtually any wielder to effectively break reality, it does have its limits. The most obvious one is a simple area of effect limitation that determines how "powerful" the wielder is - generally speaking, the more adept the Chaos Control user is, the more his powers can be focused into a smaller point or spread out across an area as the user wishes it. Even in the case of rare users that don't have any limitations at all (such as the Avatars, and the occassional mortal practitioner driven insane by persuit of the chaotic arts), they are still limited by the preconceptions of their mind, the passion in their heart and the amount of ambient chaos in the area.
While a Chaos Control practitioner can do anything they believe they are capable of, most of them never really learn the nature of this power, and as such never reach their full potential. Most people create an image of their capabilities during childhood from which all of their abilities are derived, and once the belief in these powers are cemented, it is nearly impossible to break the preconception of it - and thus, limits most people from jumping from one school of chaos to another in mid-development. Even when told bluntly the source of their power, most people aren't fully believing in it and don't advance much higher because of doubts ingrained during their growth.
One thing that can be helped to an extent, however, is their passion and the local aura of chaos. An individual's potency in Chaos Control is increased directly in proportion to the passion they feel towards their current purpose, acting as a catalyst. Even those who are technically stronger than others begin to falter when they lose their motivation and sense of purpose, and end up being overtaken who believe their actions are of the utmost importance. Coupled with that is the fact that Chaos can seep into the very atmosphere of an area when used en masse, and can in fact bolster other usages of Chaos Control just by being in an area that is inherently chaotic at the time.
Suffice to say, when a Cycle occurs, the passion in people's hearts to control their planet and maintain their species, coupled with the global chaos that ensues in the coming gobal warring, drives Chaos Control usage to crazy, unthinkable levels of power, at some times starting to rival even the Avatars themselves in sheer potency.