Mental models

Here is another example of a supermarket:

Source: http://www.peapod.com/

Although you can't smell the flowers or the rotisserie chicken in the preceding image, this virtual supermarket is no doubt designed according to specific customer expectations, what practitioners call mental models. Mental models help designers understand how customers/users think about how something should work based on their past experiences in similar situations. Without knowing the users mental model, we are simply guessing and making assumptions about what we think our users want. This is "faster horses" thinking and something we want to avoid at all costs. There is no substitute for research, observation, and testing of our solutions with real users, regardless of how certain we may feel about our work. Remember that the risk of being wrong is far greater than the time it takes to make sure we are right.