Users Arrive with Their Own Mental Models.

A common misconception in product design is the “Blank Slate” fallacy. We often assume that when a new user arrives at our homepage, they are ready to learn our unique system from scratch. In reality, no user arrives with an empty mind. They bring an “invisible manual” written by thousands of hours spent on other websites, apps, and software.

These internal templates are called Mental Models. They dictate where a user expects to find a search bar, how they believe a “Back” button should function, and the logical sequence of a checkout flow.

When a design aligns with these models, the interface feels intuitive. The user does not have to think; they simply act. However, when a design breaks these models—even for the sake of “innovation”—it forces the user to switch from automatic processing to conscious problem-solving. This creates cognitive friction, often leading to abandonment.

The governing principle of this behavior is Jakob’s Law, coined by usability expert Jakob Nielsen. It states a simple mathematical truth: Users spend most of their time on other sites.

Because of this, users prefer your site to work the same way as all the other sites they already know. This is rooted in Schema Theory, which explains how the human brain organizes knowledge into scripts to save energy. For example, an “E-commerce Schema” predicts that the company logo in the top-left corner is a home button. If a designer moves that logo to the center and makes it non-clickable, the schema breaks. The user feels a micro-moment of frustration that degrades trust.

Misalignment occurs when the “System Model” (how the database or org chart is structured) clashes with the “User Model” (how people perceive the task).

False Affordances

This occurs when an element signals that it can be used, but it cannot. A common breakdown is the “unclickable header.” Designers often style section headings (like “Latest News”) in blue or with underlines for visual emphasis. Users, trained by the mental model of the web, perceive these as links. When they click and nothing happens, the interface feels broken.

Information Architecture (IA) Mismatches

Companies often group content based on internal departments rather than user intent. A classic example of this failure occurred during the 2014 redesign of the Marks & Spencer website. The retail giant shifted from a standard catalog navigation (Mens, Womens, Home) to a “lifestyle” editorial magazine structure focused on trends.

While visually striking, it violated the mental model of a department store shopper who wanted to filter by size and price. The result was catastrophic. Online sales plunged by 8.1 percent in the first quarter following the launch, forcing the company to hastily revert to a more traditional, aligned structure.

Icon Ambiguity

Icons are metaphors, and metaphors rely on shared cultural understanding. A “Heart” icon is universally understood as “Like” or “Favorite.” However, abstract icons often fail. In various iterations of Android and iOS, the “Share” icon has shifted shapes (an arrow popping out of a box vs. three connected dots), causing measurable confusion. If an icon requires a label to be understood, it is not an icon. It is an illustration.

To ensure alignment, innovation should be reserved for the product’s value proposition, not its utility layer.

Use External Consistency

Do not reinvent standard interactions. If you are building a checkout flow, mimic the sequence used by market leaders like Amazon or Shopify. Users have already learned this script. Deviating from it by asking for billing information before shipping details will likely trigger validation errors and drop-offs.

Card Sorting for Navigation

You cannot guess a user’s mental model; you must observe it. Card Sorting is a research method where you ask users to organize your content topics into groups that make sense to them.

For example, if you are a bank, you might think “Mortgages” belongs under “Products.” However, a card sort might reveal that 80 percent of your users group it under “Buying a Home.” If your navigation labels match the user’s grouping, the cognitive load required to find the content drops to near zero.

The Scenario: In an effort to drive ad revenue, Snap Inc. rolled out a major update that fundamentally changed the app’s architecture. Previously, users had a single chronological feed for all communications. The redesign separated “Social” content (chats with friends) from “Media” content (stories from publishers and celebrities) into two different screens.

The Misalignment: The redesign served the business model, but it broke the user’s mental model. Users viewed Snapchat as a unified communication tool, not a fragmented media consumption app. The separation made it difficult to find friends’ stories, violating the core “schema” of the app.

The Result: The backlash was immediate and quantifiable. A Change.org petition demanding the update be reversed garnered over 1.2 million signatures. More critically, Snap reported a 2 percent decline in Daily Active Users (DAU) in its Q1 2018 earnings report—the first decline in the company’s history. The stock price fell nearly 20 percent. The company was eventually forced to roll back key aspects of the design to realign with user expectations.

Mental models are the invisible manual users bring to your product. Designing against them is not “disruption.” It is confusion.

The goal of user experience design is to reduce the gap between the user’s expectation and the system’s reality. When these two align, users move fast and complete tasks with confidence. Familiarity breeds trust.

This article is part of a series titled “Behavioral Science for Digital Experience Design”. The goal is understanding users through psychology, communication, and empirical research. This section focuses on Cognitive Psychology for Designers, with this article in particular covering the topic of Mental Models.