I wanted to write a note about the cognitive ease of interfaces, but I realized that such a term is out of the question.
The interface must be not just clear, but very very quickly clear. This means: no onboarding, hints or explanations — if your interface needs them, then you have already lost. A person should instantly understand where he is and what is wanted from him.
But how to manage without onboarding? Probably, in some products they are essential. Somewhere the user is ready to spend his time learning the interface, and somewhere the product is driven by other things.