Isn't there a name for this kind of fallacy? It's on the tip of my tongue. There was an anecdote (an example, rather) where each member of a family wants to go outdoors while assuming that everybody else will choose to remain indoors, and, out of being "considerate", everybody chooses to remain indoors. Comedy or tragedy ensues.

Edit: Found it: Pluralistic Ignorance. http://en.wikipedia.org/wiki/Pluralistic_ignorance. Uncited, but interesting statement: "...Pluralistic Ignorance can be caused by the structure of the underlying social network, not cognitive dissonance."