When a user lands on a site, they have certain expectations for where elements like the search function might be located, what steps they may need to follow to accomplish their goal, or what would happen if they clicked on something, we refer to these expectations as their mental model. A mental model is what the user believes about a system such as your website. And this model isn’t based on facts, but is instead constructed primarily on the person’s past experiences and what they think they know about the system.
These beliefs affect the way we need to design because people base their actions according to their mental model. So when the system doesn’t work the way people expect, they get confused. For example, a really common mismatch I’ve seen in usability testing revolves around people’s mental model for the browser back button. People believe that the back button will always take them just one step back to the previous state of the system. That’s their mental model. Unfortunately, this doesn’t always work as they expect. Sometimes people hit the browser back button to get back to the page after a modal window has opened.
But because the model window wasn’t a New York URL, they end up being taken back off that page entirely, which to them seems like two steps back. Or maybe a page was opened in a new tab, which they didn’t notice, and suddenly the back button isn’t available at all. So when a mismatch in the user’s mental model and the system occurs, it can be really difficult for people to recover or understand what to do. And even when people can understand what happens, it often makes them feel bad for making that mistake. Or it might seem like your site is broken and that lowers their perceived value of the site. Respecting people’s mental model is really the foundation of designing usable, user centered systems. It’s important to conduct research and find out what are users. Mental models are to make sure we design the system to match those expectations.