“A key principle within usability is that people carry around a ‘mental model’ of how we expect the world to behave. These models are based on past experiences and can be a very powerful factor in influencing how people behave in certain situations. In our experience of usability testing, usability suffers when a site does not match users’ expectations. Indeed, our usability testing sessions have repeatedly shown that breaking expectations makes users unhappy.” (Tim Fidgeon ~ Spotless Interactive) courtesy of usabilitynews