Walking was long treated as a hard planning problem, until a simpler idea took hold: a body with the right dynamics almost walks on its own. Tedrake's toddler learned to walk in about twenty minutes by adding a little actuation to a passive walker rolling down a ramp. A central pattern generator is that idea in software, a small set of coupled oscillators that produce the rhythm of a gait, hip and knee cycling in phase. You are not scripting every footfall; you are setting a rhythm and a well-timed push, and letting the pendulum dynamics of the legs handle the rest.