Complexity and chaos are not the same. Complexity requires a higher degree of order and works against chaos. To construct a complex system, work is required - resisting or decreasing entropy. Chaos increases entropy and is a natural process of the universe. - Alexander B. Alleman, PhD student, Montana State University
Managing projects in the presence of uncertainty requires energy be put into the system to maintain it's equilibrium and stability. How much energy, for how long, in what order, in what type is the role of management. To know the answers to these question of how much, when, where means make estimates of those quantities and the resulting outcomes that reduce chaos.
In other domains, this principle is called the 2nd Law of Thermodynamics. In project work, this principle is also applicable, since the system of work is a dynamic coupled collection of random processes, interacting with each other in non-linear, non-stationary ways.
The Law of Entropy is expressed in this 2nd law. The law predicts that the natural state of all things—from the tiniest atoms to the largest of galaxies—is that of disorder. This means, without appropriate systems or balances in place, everything wants to fall into chaos. The management of this naturally occurring (statistical) - as well as the probabilistic - set of processes is the role of Risk Management. If there no uncertainties on your project the 2nd Law would not be applicable. Since all project work is uncertain there is ALWAY risk associated with those uncertainties. And of course managing in the presence of these uncertainties Mandates making estimates about the impact of managerial actions on the outcomes of those decisions.
A nice background on the 2nd Law of Thermodynamics of Project work comes from Shim Marom. This topic is little understood in some SW and IT domains. In Engineering and Construction and Software Intensive Systems is it a well known process.
The entire Universe and everything in it is a collection of 2nd order non-linear partial differential equations, all obeying the 2nd Law of Thermodynamics.