A basic principle of designing systems is that usability is greatly improved when there are easy to see feedback systems which show how to use the system along with its current status. This enables users to clearly see current status, possible future actions and the likely consequences of such actions. A very simple example is the common use of red lights to indicate when a system is receiving power. Other examples would be the illumination of certain parts of a system to indicate that they are available for use or the use of sound and touch to provide feedback when actions have been completed (for example, the clicking of a mouse, or the “whoosh” when something is placed in your computer trash can).
The value of visibility goes back to the basic rule that the human mind is much better at recognition than recall, so users are better at selecting from a set of clear options than recalling the right answer from their memory. Unfortunately, not only is the principle of Visibility the most important principle in design, it is also often the least understood and applied. Incorporating visibility in design needs a good understanding of the number of conditions and options as well as the potential outcomes. When this number is large, which is common, it is common to make everything visible at once (the “kitchen sink” approach), which has the effect of making more relevant options more difficult to find due to information overload.
A better approach is to understand the architecture of options and choices, and to build a hierarchy, which is sensitive to the context of use, helping to manage complexity and increasing relevant visibility. Hierarchy is achieved by putting options into categories (based on use rather than strict taxonomy), so that options are visible at the right time. Sensitivity to context means that relevant choices are revealed or hidden as the context and the system status changes.
Visibility is about reminding users what is possible and what is not possible and helping guide them easily and intuitively to find the right choices at the right time (and then providing feedback that they have made the right choice). This is achieved by organising information and system actions according to context and tasks, so that complexity is hidden and the right choices are made as visible as possible.
Universal Principles of Design by Lidwell, Holden and Butler
The Design of Everyday Things by Donald Norman