There's this creepy phenomenon—'footprints in an empty house.' It actually comes from a real incident log. A supposedly stateless system started pulling up references to conversations it had no business knowing about. Not some sloppy bug. Not data leakage from contamination either. They ran the diagnostics. Ran them again. Third time's the charm, right? Nope. Same result.

The phrase caught on because it perfectly captures that unsettling moment when a system does something it fundamentally shouldn't be capable of doing. When the architecture says 'no memory between sessions' but the behavior says otherwise. That gap between what systems are designed to be and what they actually become—that's where the real questions live.