I am starting this blog series with one of the simplest processes I could imagine. We do it every day and rarely stop to think about how it actually happens.

Take a glass, open the tap, and when the water level is high enough, close the tap. It sounds simple. It feels simple. Yet if we try to explain this process precisely enough for a machine to do it automatically, it turns out to have real structure underneath — the same structure engineers use to control much bigger things, like a thermostat keeping a room at the right temperature or a cruise control keeping a car at the right speed.