Usability
Too big a topic to fully explore here - just remember where ever there are humans ( or other sentient beings ) in the mix - design intent does not always go according to plan.
Design intent does not always align with how it is used.
As soon as you have designed something test it, then test it again and again.
What is logical to you - the designer / planner - may not make sense to the user.
and if a design or a technology isn't Usable - it doesn't get used.
From a very successful Technology company. The calculating and cunning founder of Apple.