Memory as a belief state

The "Practical Guide" gives a formal framing that is more useful than it first appears. It describes agent memory using a POMDP structure, where memory functions as the agent's belief state over a partially observable world.

Unpacked: the agent cannot see everything about the world at once. So it builds and maintains an internal model of what it currently believes is true. That internal model is its memory. The practical consequence is sharp: if the memory is wrong, every downstream decision degrades. This is why later chapters spend so much effort on keeping memory accurate. A wrong belief state quietly poisons everything built on top of it.