The Closed World Assumption

Logicians call this the closed world assumption — the belief that your list of possibilities covers everything. It works in limited domains:

• Math proofs — you can enumerate all cases in some problems
• Binary questions — "Did the switch flip or not?" has exactly two answers
• Card games — a finite deck means eliminated cards are truly eliminated
• Chess — all possible moves are known

But most real-world problems are open-world. Diseases you have never heard of exist. Motivations you cannot consider drive people's behavior. The universe is under no obligation to limit itself to possibilities you have considered.