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:
Consistency
Peculiarity
Cognitive load minimization
Actions minimization
Errors protection
Avoiding hidden logic
Predictability
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.