Lessons from "The Design of Everyday Things" by Don Norman
Constraints: "when instructions have to be pasted on something (push here, insert this way, turn off before doing this), it is badly designed." To make something easy to use, design it so that it can only fit one way. What is a good example of this in user experience? The home button on the iPhone. The Home button is a shortcut to take you to the home screen. In contrast, on an Android phone, there are 4 ways to get to the home screen. As a result, iPhones are known as the simple phone, while the Android is known for power users. The author, Don Norman is incredibly witty. He shudders in apprehension when companies insist on building products that let you turn on the air conditioner, start filling the bathtub and make a cup of coffee while you are driving home. The proliferation of such features cause confusion and distractions.
Visibility indicates the mapping between intended actions and actual operations. To indicate what parts operate and how, to ultimately show how the user should use it. An excessive amount of visibility is intimidating. Lack of visibility is also just as frustrating. It goes back to Goldilocks and the Three Bears, finding just the right amount is a fine balance and based on trial and error.