Now we know all components of interaction. And it is time to define, what makes the interaction with user interfaces effective.
Effective UIs allow the user to interact fast and with less errors. This is possible if the UI satisfies the following criteria:
Cognitive load minimization
Avoiding hidden logic
Ease of study and findability
These criteria are controversal, so the principal task of UX design process is to find the optimal balance between them.
Next: User experience lifecycle