UI design is the visible layer of a product: typography, colour, spacing, icons, motion and visual hierarchy. It carries the structure to the user and makes a product feel considered in the first two seconds. Strong visuals over a broken flow still fail, though weak visuals can hide a good flow completely.

One is what you see, the other is what happens to you. In a restaurant, the interiors and the menu design are the interface. How easily you find a table, order and pay without asking for help is the experience. One is judged in two seconds, the other on the second visit.

No, though it delays the discovery. A polished interface buys you trust for the first minute, which means the user gets further in before they hit the wall. That usually makes the drop off worse, because they had invested something by the time it happened.

Looks are not the test. Check whether traffic converts, whether users drop at one repeated step, and whether support answers the same question every week. If the numbers are healthy, buy the visual refresh and enjoy it. If they are not, no new colour system will move them.

No. The same thinking applies to an ATM sequence, a restaurant menu, a hospital signboard, a form you fill in at a counter. Anything a person has to get through has an order, a set of decisions and a failure state. Screens are just where most of the money is.