Interface design is not only visual styling. It shapes what users notice, understand and do. Clear hierarchy, familiar patterns and immediate feedback reduce the amount of information people must keep in working memory.
Good interfaces prevent errors before they require an error message. They use sensible defaults, constrain dangerous actions, explain consequences in plain language and make recovery possible when something still goes wrong.
The effect should be tested with real tasks rather than judged from a static screen. Measure completion time, hesitation, mistakes and support questions, then improve the points where the interface and the user’s mental model diverge.