As systems add more functionality, they become more complex. As systems become more complex, the traditional processes we use to manage those systems become more strained. The typical response on the part of those building these more complex systems is to try to understand how to scale up the processes from those that can handle simple systems to those that can handle complex systems.
Consider a "simple" system A with only 100 functions. Say process X has been used to successfully manage A. Process X could be Agile Development, RUP, Earned Value Management, or any other of your favorite management processes.
Now we need to build a more complex system B with 1000 functions. Since B has 10X the functionality of A and we know X works for A, most assume that we can use X to manage B as well, although we assume that it will take 10X the effort.
The flaw in this reasoning is that the difficulty of applying X to B (regardless of what X is) is proportional to the complexity of B, not to the functionality of B. And when the functionality increases by 10X, the complexity, because of the exponential relationship between functionality and complexity, actually increases thousands of times. The exact number is highly dependent on the nature of the functions of B and how they are organized, but the number will typically be very large.
As long as we focus on how to better use X to manage B, we are doomed to failure. The complexity of B will quickly outpace our ability to apply X.
Instead, we need to focus on the real problem, the complexity of B. We need to understand how to architect B not as a single system with 1000 functions, but as a cooperating group of autonomous systems, each with some subset of the total functionality of B. So instead of B, we now have B1, B2, B3, ... etc. Our ability to use X on each of Bi where i = 1, 2, ... will be dependent on how closely the complexity of the most complex Bi is to the complexity of A (which is the most complex system on which X is known to be a viable process.).
The bottom line: if we want to know how to use process X on increasingly complex systems, we must focus not on scaling up the functionality of X, but on scaling down the complexity of the systems.
For more information on scaling down complexity in IT systems, see my white paper, "The IT Complexity Crisis" available at http://bit.ly/3O3GMp.