A UX designer's guide to the Principle of Least Surprise

From the moment we wake up to when we hit the hay, we rely on websites, apps, and digital tools to navigate our lives. When they function smoothly, they're like helpful guides, making our lives easier and more enjoyable. But when our interactions with digital tools lead to an unexpected result, we can quickly become irritated and confused.

To avoid such user friction, apply the Principle of Least Surprise (POLS) to your software designs. 

POLS is a guideline that says any user interface (UI) should operate in a manner that surprises the user as little as possible. Sometimes referred to as the Principle of Least Astonishment (POLA) or the consistency principle, this rule minimizes the learning curve of a product to improve user convenience.

Imagine you're using a food delivery app to order dinner after a long day. You've carefully selected your items, added them to your cart, and proceeded to checkout. Everything seems to be going smoothly until you reach the final step. Expecting to see a clear and prominent "Place Order" button, you click on what appears to be the logical choice, only to find yourself redirected to a page with irrelevant information or worse, back to the beginning of the ordering process. This unexpected outcome leaves you frustrated and uncertain about how to complete your order.

A product that frequently surprises users can be hard to navigate. While innovation is essential for the evolution of technology, attempting to reinvent the wheel in a user interface (UI) will likely lead to poor engagement rates and negative reviews.

The disconnect between your expectations and the actual outcome highlights the importance of using the Principle of Least Surprise (POLS) in digital product development.

The psychology behind POLS

Our brain relies on past experiences to predict how things will behave. For example, when you've learned to type on a QUERTY-style keyboard, you depend on muscle memory to land on the correct keys. Similarly, if you double-click a computer mouse, you expect to open a document. If you frequently shop online, you anticipate a short series of steps at checkout.

However, when the actions you're accustomed to yield unexpected results, you feel surprised and frustrated. The mismatch between the outcome of an action and the expected result is “cognitive friction.” It requires the user to slow down and learn a new action to achieve the intended result.

Since users are seeking convenience, they're likely to reject an unconventional design rather than learn to use it. To avoid customer churn, product teams strive to increase predictability and minimize surprise.

Why does the Principle of Least Surprise Matter? 

Anything that keeps a user from accomplishing a desired action on a website or app is “user friction.” When users experience friction, they feel confused and frustrated, often prompting them to give up.

An estimated 21% of shoppers leave an e-commerce site due to a complicated or lengthy checkout process. The numbers are even worse for mobile apps; 90% of users stop using an app due to poor performance, and 86% have deleted or uninstalled at least one mobile app because of performance problems.

By incorporating POLS into your software design, you can minimize user friction and prevent customer turnover.

What is an example of the Principle of Least Astonishment?

You depend on the Principle of Least Astonishment every day without even realizing it. For example, when you approach a door with a handle, you automatically pull to open it. When using an app, you intuitively recognize the symbol that signifies a menu and hover over it to seamlessly navigate a site. When the menu appears as expected, the designer has incorporated POLA into the UI.

Consider the value of a Save button. If an application uses an unexpected icon or term for this, the user is likely to experience frustration when attempting to save progress. The unexpected reference requires the user to spend time searching for the right term while facing the risk that clicking the wrong icon could lead to the loss of the item. 

UX designers have substantial knowledge that can make it difficult to not assume how users will interact with a product. When you follow specific strategies to incorporate POLS into your UX design, you take the guesswork out of how to eliminate surprises for users.

The following tips can help you naturally integrate POLS into your UX design.

Use familiar patterns

Recognizable patterns and icons, such as consistent navigation structures and clear information architecture, help users enjoy seamless interaction with software applications, enhancing usability and user experience. When designing interfaces, it's crucial to consider these established patterns and adhere to them whenever possible.

For instance, while a shipping box might be a more accurate representation than a shopping cart on an e-commerce site, shopping carts are what users expect to see. Departing from such norms requires extra effort from your customers.

By aligning with familiar patterns and interfaces, you create a sense of comfort and familiarity for users, enabling them to navigate your software with ease. This doesn't mean you can’t innovate, but carefully consider any departure from established norms and thoroughly test to ensure it enhances rather than detracts from the user experience.

Stay consistent across platforms

If your service exists on multiple platforms, check it works the same way in every location. Whether using a website on a PC or a mobile app on a smartphone, users want to have the same convenient experience.

Prioritize clarity over style

A fancy design can make a website or app more engaging, but it will only take users so far. Your customers’ primary expectation of your software is good functionality, so this should always be a top priority.

Design with a clear, straightforward interface in mind, and incorporate everything else to support it.

Make core actions easily available

The design of your user interface should highlight its intended function and make it easy to achieve the overarching goal. For example, if your app is designed to find the nearest public transport, a map should be immediately available.

Conduct tests

Sometimes, it's unclear which design elements are most intuitive to users. When you're unsure of specific details, usability testing can give you the clarity you need.

Conduct UX research that allows you to observe how different groups of your target audience interact with a couple of design variations. Use metrics like time spent, error rates, and click-through rates to gauge success.

Use tools for success

There are a variety of tools to help you understand how users interact with your product. Try a combination to gain insight into design issues that impact usability.

• Prototyping tools: Used during product design, prototyping tools allow you to make quick iterations that help you apply POLS.

• Heatmaps: These help you understand where users click most frequently so you can recognize when frustration occurs. Heat maps can help you spot rage clicks, error clicks, and rapid cursor movement, all signs of confusion or frustration.

• Analytics software: By tracking user metrics, you can identify bottlenecks and points of confusion and eliminate them from your design.

• User-testing platforms: Some websites help you run usability tests to collect qualitative data that can be used to better align your design POLS.

• Feedback platforms: Gathering user feedback is critical to understanding audience expectations and creating a design that meets them.

Understanding how to incorporate POLS into your design is only half the battle. Without measurable data, you have no way of evaluating what works and what doesn't.

When you use strategies to measure user surprise and the effectiveness of your designs, you can identify areas for improvement to increase customer satisfaction.

These indicators can help you recognize whether your design is engaging or frustrating users.

• User engagement rates: Increased engagement indicates a user-friendly experience.

• Customer satisfaction score (CSAT): Customer satisfaction scores that improve after changes are made suggest your alterations are in line with POLS.

• Cart abandonment or app deletion: If these numbers are high, consider how changes in UI could reduce them. A decrease in cart abandonment rates indicates your checkout process meets customer expectations.

• Error rates: User errors are a strong indication that your interface isn't user-friendly. Measure error rates frequently to see if they decrease when changes are implemented.

• Time on task: Extensive time to complete a simple task indicates users are meeting unexpected complications. When changes reduce the amount of time users take to complete a task, your interface contains fewer surprises.

How to quantify "astonishment" or confusion

Sometimes, it can be difficult to recognize when your interface fails to meet user expectations. Without insight into the user experience, you can't learn what elements are causing bottlenecks or frustration.

These tools can help you gather measurable data to quantity user surprise:

• Heatmaps: Areas of the screen with heavy interaction indicate which elements are used most. Areas with less interaction can suggest that certain elements aren't functioning as expected.

• Exit-intent surveys: Exit-intent surveys can do more than quantify satisfaction. Use them to directly ask users what navigation elements were most confusing.

• Session recordings: The ability to observe where users hesitate or make errors can highlight problem areas that fail to meet user expectations.

• Behavioral analytics: By tracking how often users exit particular screens, backtrack, and abandon tasks, you can measure user surprise for specific functions.

How can beta testing help with POLS?

It can be difficult for a tech company to stand back from a project and get a clear view of what will surprise users. Beta testing allows designers and developers to gather user feedback about how a system behaves. Users test the software in real-world environments and provide specific insights about how it fails to meet their expectations. You can then use this information to make the system more intuitive and user-friendly.

Since users tend to have similar expectations from their interactions with a digital product, a small test group is usually sufficient to recognize areas where POLS is absent. Using tests with at least five users from your target audience, 85% of issues can be solved. If you have multiple user personas, you need a sample of five people per persona.