Complexity theory postulates that change is emergent rather than pre-determined. Organized efforts to direct it confront the impossibility of our ever understanding the totality of a system that is in constant flux. Composed of innumerable elements, continuously shaped and reformed through interaction upon each other, the system is constantly creating new elements that in turn may affect (loop back) and change those already in existence. Thus we cannot predict all the effects that any of our actions may have on the wider system or indeed on ourselves as initiators of the action. Small ‘butterfly’ actions may have a major impact and apparently significant ones may have very little.
Read more here.