Another example from my stay at the conference. I had a Board meeting in the Japanero room. The hotel meeting rooms were arranged alphabetically, so the Japanero room was easy to find, right between the room beginning with 'I' and the one beginning with 'K'. A colleague asked where we were meeting. I said "the 'J' room". He had no clue what I was talking about.
This illustrates a pretty good example of how an incorrect user model can lead to a poor design. I made an incorrect assumption of his domain knowledge. Because he was a Board member, I assumed he got the same tour I did, which explained the alphabetical design (or he would have figured it out on his own by then). I also made an incorrect assumption about the quality of my message. I also assumed that saying "the 'J' room" would be enough of a semantic link to the organization of the rooms that he would understand my meaning. Because the alphabetical organization was a salient part of my schema, the statement was enough to activate it. But that is no guarantee for other users.