Comment by Raphmedia

People won't see it when looking at you app with blinders on. However, they will feel the difference when using the competition's app.

They won't be able to tell you why they prefer the one with more time invested in the UX/UI, but they will almost always choose that one.

There are universal rules in design and everyone is using them. We are actively training the users into feeling those rules as superior.

(This is also why huge paradigm changes feel so refreshing. Breaking the rules on purpose is very strong.)