Don't look behind the curtain

In Threads - Threat or Menace Eric S. Raymond writes that "Threads are a fertile source of bugs because they can too easily know too much about each others' internal states". I wondered whether this applies to people as well: can you get more errors if the people on a (large) team know too much about each others' internal states? Is this what prevents XP from scaling well beyond teams of 10-12? And what is the team size where an event-driven style of interaction and collaboration becomes a more efficient way of working?