Things you think everyone knows

This morning I exchanged mail with Jon B., one of my old bosses, and at some point I explained I would be out of the country soon. There ought to be a name for the phenomena of thinking that a fact is well-known when it isn't. At this point, it seems like I've been talking about the camino for so long that I assume that most people know about it and know I'm going. And then I'm reminded that it's simply not true.