What does it mean that mental inventory is always incomplete?

Your sense of cognitive completeness is an illusion. What you can access at any moment is a context-dependent sample of what you actually know — and the sample changes without your awareness.

Example: Ask yourself to list every active commitment you have right now. You'll produce a list that feels fairly complete. It's missing at least 30-40% of the actual items. The items aren't gone — they're in long-term memory — but they're not in your current retrieval set. What's worse: you don't feel the gap. The list feels complete because your brain treats available information as all information.

Try this: Do a full brain dump. Set a timer for 15 minutes. Write down every open loop, task, commitment, worry, idea, and half-formed plan. Don't organize — just dump. Count the items. Wait 24 hours and do it again. Compare the lists. Items that appear on one but not the other were always there — just not accessible in that context. That's incomplete inventory in action.