Summary: What is a Forcing Function in interaction design? A forcing function constrains a user, forcing them to complete a task.
In short, they force users to take an action (you force), usually for safety reasons. Forcing functions to help streamline, simplify, or minimize how a user interacts with a design. Designers benefit from this interaction design technique by reducing navigation redundancy, task effort, and the complexity caused by “feature frenzy”
Not all forcing functions are based on good design decisions. Successful designs that use the forcing function interaction design technique are based on an empirical understanding of user default behavior, task expectations, error and failure analysis, and context of use observations.
When to use Forcing Functions in your design?
Use a Forcing Function in your design only if you want to:
- Constrain a user interaction
- Speed up or re-direct a task
- Limit an interaction
- Eliminate confusion
- Simplify a design
- Protect users from danger or hazards (safety)
Important: Only use a forcing function when you have thoroughly studied user behavior, tasks, environment, and context of use.
When do they go wrong?
Feature-forcing (making users interact with features they don’t want) tends to result from inappropriate use of the forcing-function technique. A forcing function is a disciplined use of force, the way a mother would give her child what they need, not what they want.
The two extremes of forcing functions are too much force and too little force. An example of too much force is like making a user interact with implicit rules, hidden actions, or conceptual models (UI patterns) that are unnatural. An example of too little force is making a user ‘hunt around’ to make something important happen (also a potentially inappropriate use of the progressive disclosure interaction design technique).
Getting the right balance of force is important. Force can be a powerful design tool, but it can also be oppressive: poor user adoption is often the result of force that is difficult for the end user to get used to. When designing a forcing function, there needs to be a good reason (user-validated) to justify the use of the technique.
In general, products that lack good usability are characterized by designs where users are more error-prone, where defaults are inexact, and where layout or instinctive behaviors don’t feel right. In general, designs that include error recovery and handling as a strategy avoid forcing functions. This isn’t to say error handling is bad; it’s just that error prevention often should be the focus, not error recovery.
See How relying on user education is a failed product management strategy
This is a change of philosophy to most Product Development. Deliberate use of intuitive UI’s with deliberate and ethical forcing functions says:
Making a user do something in an elegant way is far better than a mediocre way that also offers them support as they recover from the error. One is empowering, the other is patronizing from a wider user experience perspective.
Why are Forcing Functions used?
Forcing functions comes out of user advocacy in Human-centered design. A forcing function should feel natural and transparent to the user. Users should never question why there is no “choice” in completing their task. The “dead-end” or directive action required should seem natural and protective either by the product experience or the interface that limits all other options in that momentary task.
These case study examples illustrate how forcing functions work
A razor blade company, after watching women shave their legs in the shower (researchers had them wear swimming costumes), realized that a design flaw would potentially cause the razor to slip, leading to dangerous cuts (and lawsuits). Designing the razor handle and blade for wet hand use was need to prevent cuts.
The forcing function was a safety design handle now common in shower razors.
After observing truck drivers driving on the highway, an automotive manufacturer realized that an incoming email, while driving–could only display two sentences of text before resulting in driver distraction and an accident. The messaging system only displayed a brief two-sentence summary of messages while the vehicle was in motion. However, the full message was accessible once the vehicle came to a stop.
The forcing function was a rule (policy) of two-line messages requiring drivers to safely stop to read full messages.
Conclusion
Forcing functions allow a design to follow user intuitions based on their expectations derived from studying their behavior, environment, and context. However, designers should take precautions against imposing this powerful interaction design technique without first understanding the user task flow, context of use, and error scenarios involved.
