The Nature of User Errors

The gulfs of evaluation and execution are critical concepts in understanding how users interact with technology:

• The gulf of evaluation is the challenge users face in understanding the system's current state. For example, consider users interacting with a modern smart thermostat. If the thermostat’s display and menus are not intuitively designed, users may struggle to evaluate its current settings.
• The gulf of execution is the difficulty in performing actions to achieve desired outcomes. For example, users may find it difficult to figure out how to adjust the temperature to their comfort level.

Both gulfs represent the distance between the goals of users and what they can actually accomplish with the system. These gulfs can lead to a frustrating cycle of actions and evaluations as users attempt to align the system with their goals. Effectively bridging these gulfs in design enhances usability, making technology more accessible and satisfying to use.

Mistakes in user interactions often come from a disconnect between what users expect from a system and how it's actually designed. If users have a wrong idea about how the system works, they might use it incorrectly. For example, if users try to delete an email but the delete icon looks unusual or unclear, they might end up archiving the email instead. This happens because the interface doesn't clearly show how to perform tasks (gulf of execution) or how the system responds to these actions (gulf of evaluation).

Assuming that users will just learn to understand a complex system is not a good strategy. If a system is too hard to use, people are likely to give up and go somewhere else. That’s why it’s crucial to align the design with what users already know and expect, helping to prevent mistakes and improve overall satisfaction.

Discovering gaps between users' mental models and designers' mental models is crucial for creating intuitive interfaces and avoiding user mistakes. This process involves collecting user data through various research methods tailored to different stages of design development.

• Early design stages: Methods like contextual inquiry, field studies, and ethnographic studies involve observing and interacting with users in their natural environment. These approaches provide deep insights into their behaviors, expectations, and how they think a system should work. This can reveal crucial information about what users naturally expect from the product, helping to align the design more closely with these expectations.
• Later design stages: Once a prototype or system is in place, qualitative usability testing becomes key. This type of testing allows designers to watch users interact with the product in real-time, noting where they struggle or make errors. This direct observation helps identify where the product's design does not match the user's understanding or expectations.

Slips are errors where users intend to perform one action but inadvertently complete a different, often similar one. For example, clicking "Reply all" in an email instead of "Reply" is a slip or accidentally selecting "Print 10 copies" when you intended to print just one.

Slips generally happen when users are not fully focused on the task, typically operating on autopilot. They frequently occur with experienced users who are very familiar with a task's processes, i.e., they understand the goal and the steps involved but occasionally take a wrong step due to a lapse in attention.

Conversely, mistakes occur when users have a misunderstanding about how to perform a task or implement it wrongly, often seen with newer users still learning a system’s functions.

Constraints in user interfaces serve as effective tools to prevent slips by ensuring users can only make choices that are valid and intended. This helps prevent errors and enhances usability by simplifying decision-making processes. For example, when filling out an online form to schedule an appointment, the interface might constrain input by allowing users to select times only within business hours. This prevents the common slip of scheduling a meeting at an unavailable time. The system could automatically gray out or remove times outside of business hours, ensuring users only choose from viable options.

Constraints guide users smoothly through tasks, preventing mistakes and making interactions more straightforward and error-free.

Suggestions from a system can significantly reduce slips by guiding users toward correct actions before errors occur. This proactive approach enhances usability by aiding in accurate data entry and navigation. For instance, consider a mobile banking app where users frequently transfer money. Typing account numbers or account holder names manually is prone to errors. To help prevent these slips, the app might suggest saved or recently used accounts as users begin typing, enabling them to select the correct account without entering the full number or name. This not only speeds up the process but also minimizes the risk of sending money to the wrong account.

Good defaults play a crucial role in preventing slips by setting reasonable initial values that guide users toward correct selections. This not only facilitates a smoother interaction but also educates users on typical choices, enhancing their understanding of the options. For example, consider software installation wizards, where choosing the "standard installation" option as the default helps users who might not be familiar with custom settings to proceed with confidence. This default choice typically includes the settings most users will need, reducing the risk of incorrect installations.

However, it's crucial to avoid using defaults as a dark pattern where choices are set to lead users into making decisions that benefit the service provider more than users, such as opting into email subscriptions unknowingly. Good defaults should always align with what is most likely beneficial and expected by users, ensuring a helpful and ethical user experience.

Reducing the memory burden to prevent slips and mistakes involves minimizing the amount of information users must remember while completing tasks. This approach is especially helpful in environments where distractions or multitasking are common.

Even if users are interrupted, they can quickly and accurately resume their tasks, making the interaction with the system more efficient and error-free. For instance, imagine users booking a multi-city flight. A well-designed booking system will keep a visible summary of all chosen destinations, dates, and flights as users add each leg of their journey. This prevents users from having to remember each selection or from booking duplicate flights for the same date.

By continuously displaying this information, the system helps users verify their choices at each step without relying solely on memory.

Confirmation dialogs serve as a crucial checkpoint to verify users' intentions before proceeding with potentially irreversible actions. For instance, imagine users managing files in a cloud storage app. If they select multiple files and hit the delete button — perhaps mistaking it for the download button — a confirmation dialog that asks, "Delete these files?" gives them a moment to pause and reconsider their action. This simple interaction helps prevent the accidental loss of important data.

However, it's important to use confirmation dialogs judiciously. Overuse can lead to dialog fatigue, where users become so accustomed to dismissing confirmation dialogs that they no longer pay attention to the content, potentially leading to the very errors the dialogs are meant to prevent. Therefore, they should be reserved for actions with high consequences to maintain their effectiveness and prevent workflow disruption.^[2]

Don't place the confirmation button in the same spot as the initial trigger button that triggered it. For example, if a user clicks "Delete" in the top-right corner, the "Confirm delete" shouldn't appear in that same position. Users in a hurry might accidentally double-click or tap twice in the same location, inadvertently confirming an action they meant to reconsider. By spatially displacing the confirmation (perhaps centering the dialog with buttons in a different location) and introducing a brief temporal buffer, you create a more deliberate decision-making moment that better protects against accidental data loss.

The “Undo” option in user interfaces allows users to easily reverse actions and acts as a safety net, reducing the stress and consequences of errors. For example, consider users hastily sending an email before it's fully ready. If they realize a mistake right after hitting send — perhaps forgetting an attachment or needing to correct information — an “Undo” option available for a brief period allows them to retract the email. This capability saves them from potential embarrassment or miscommunication and is a feature appreciated by many users of popular email platforms.

By incorporating this feature, you acknowledge that users are human and prone to errors, particularly when multitasking or working under pressure.

By offering contextual error warnings while users input data or make selections, systems can guide users toward correct actions without disrupting their workflow. This proactive approach to error management not only saves time but also improves user satisfaction by making interactions smoother and more intuitive. For example, imagine users filling out an online payment form. If they enter an expired credit card date, the system immediately highlights the error and displays a message like "Please check the expiration date." This instant feedback prevents users from submitting the form with incorrect information, avoiding transaction failures and the extra time needed to correct the error.

For more complex validations that may require extensive effort, such as password inputs, a simpler method is to provide helper text where mistakes are most common. This text can guide users in creating valid passwords by specifying requirements like character count and symbol use before they start typing. Helper texts help prevent errors right from the start.