Law of inventory: the more accurate you try to make your inventory, the less accurate it becomes
This is one of the paradoxes of the map vs the territory.
Companies used to (and some still do) spend a lot of time doing periodic inventory counts and recounts trying to reconcile their computerized inventory system with what people find in the physical inventory. The problem is that counts and recounts are subject to error, no less and sometimes more than the original inventory transaction records. And when companies did these recounts, they usually tried to freeze the computerized inventory system, which of course they were willing to do for a limited timespan.
Inventory is usually in motion, or the organization is not doing anything. Which means the best you can get in a computerized record is an approximation. It's a lot better if the inventory is touched only by robots but:
- computer bugs
- people manually taking things either because they need them for a legitimate process or for whatever other reason
- lots of other kinds of losses: breakage, spoilage, whatever.
This "law" also applies to any attempts to model and record physical reality-in-motion in great detail. Get over it.