There are plenty of successful applications with bad UIs. Also, business logic is encapsulated in code - if that's borked, no amount of UI will save it.
Because data >>> UI >> code.
> Also, business logic is encapsulated in code - if that's borked, no amount of UI will save it.
The assumption here is that the bare minimums are fulfilled. If the software doesn't work at all you have none of the above.