Protect Primary Uses

When I try to add secondary functionality to a widget and it doesn’t feel right, I begin thinking through how to change primary functionality to accommodate the new stuff. Often that leads to a poorer experience for the primary uses of that widget.

Avoid this first by resisting to add non-primary functionality. If you’ve resisted all you can, before diving into the design for the secondary functionality, make sure to document the primary use cases. For each design iteration go back through the primary use cases, and make sure the experience is still great.