I mean, I literally said "economic theory", the basic idea is that you simplify the assumptions to make a point. That's literally what most of economics is! In

I mean, I literally said "economic theory", the basic idea is that you simplify the assumptions to make a point. That's literally what most of economics is! In the real world, the assumptions are weaker and the dynamics are much more complicated than a toy model, but you can still transfer the same conclusions - in this example, that pension requires making babies and that without a good negative feedback mechanism, the system eventually collapses.