The concept of ergodicity is something people get intuitively but unlearn by visiting a statistics class or completing an MBA. The distinction between ergodic and non-ergodic systems is nonetheless essential for understanding how humans act and why some “irrational” behavior or heuristic might be rational after all. It is a concept mostly used in mathematical probability theory but originated in thermodynamics.

An ergodic system is technically defined as a system that has the same behavior averaged over time as it has averaged over the space of all the system’s states. This might sound complicated at first, but the difference between ergodic and non-ergodic systems can be illustrated in two examples—rolling dice and Russian roulette.