Conservation Laws
In physics, there are Conservation Laws, which are among the most important discoveries mankind has ever made. The great-granddaddy is Conservation of Energy, that energy can neither be created nor destroyed. An unexpected energy imbalance has driven a lot of physics; for instance, neutrinos were discovered mathematically long before they were actually detected because of an energy imbalance in beta decay.
In the human social world, the conservation laws are not so obvious. But I'm increasingly of the opinion that there are many quantities that are quasi-conserved across years and decades, with a balance that accurately reflects the deposits and withdrawals made against it. I say quasi because they are quite as pure as Physics conservation laws, and they usually involve fundamentally innumerate quantities anyhow. But they still come close to a conserved quantity for it to be useful for understanding things in the real world.