[…] Why do collapses happen? Tainter argues persuasively that societies collapse when marginal returns on complexity begin to decline.

Complexity is a problem-solving tool. We can reap tremendous benefits from complexity. But complexity is also quite expensive. If you’re working as, say, a scientist, someone else is laboring to sustain your life—the food you eat, the clothes you wear, etc—while you engage in research. The more specialized we become, the more those primarily producers must produce to keep everyone else fed and clothed, the more resources we must pour into coordinating and communicating and transporting.

And sometimes, we find that additional complexity begins to generate declining marginal returns—fewer returns per unit of resources invested in complexity. We begin to invest more and more just to sustain things as they are, and when we reach that point and face some new crisis, we have no surplus left to invest in more complexity. […]