Complexity breeds complexity. There are a whole set of secondary causes of complexity. This covers all complexity introduced as a result of not being able to clearly understand a system. Duplication is a prime example of this — if (due to state, control or code volume) it is not clear that functionality already exists, or it is too complex to understand whether what exists does exactly what is required, there will be a strong tendency to duplicate. This is particularly true in the presence of time pressures.
Within a few hours of reading that quote I had a conversation illustrating it. I talked with someone who needed to make a small change to a complex section of code. He said the code had three minor variations on the same chunk of functionality. He could get his job done much faster in the short term if he simply added a forth mutation to the code base. He refused to do that, but many developers would not refuse.
Suppose the rate of growth in complexity of a project is proportional to how complex the project is. And suppose, as the quote above suggests, that the proportionality constant is the time pressure. Then the complexity over time is given by
y‘(t) = a y(t)
where y(t) is complexity at time t and a is the time pressure. Then complexity grows exponentially. The solution to the equation is
y(t) = y0 eat
where y0 is the initial complexity. This isn’t meant to be an exact model, just a back-of-the-envelope illustration. On the other hand, I’ve seen situations where it gives a fairly good description of a project for a while. Complexity can grow exponentially like compound interest, and the greater the pressure, the greater the rate of compounding.
Now suppose there’s a different kind of time pressure, a pressure to simplify a project. This would correspond to a negative value of the proportionality constant a. If there were such pressure, this would mean that complexity would decrease exponentially.
I don’t think this kind of negative pressure on complexity is as realistic as positive pressure, but it’s not entirely unrealistic either. In the rare case of pressure to simplify, removing one source of complexity could lead to cascading effects. Because we don’t need this one thing any more, we don’t need these other things that were only there to prop it up, etc. There could be a sustained decrease in complexity, though it probably would not be exponential.