You can design something to be 100% usable and logical to your end-user, but if the product is dull-as-dishwater people may still have no interest in using it. Don’t underestimate the irrational side of people; the importance of warm fuzzy feelings. (And that’s why I feel user testing is a double-edged sword; it often ignores the unquantifiable qualities of design. But that’s a discussion for another article).
The Tao of user experience design is a concept called “flow”. In a perfect user experience all tasks flow seamlessly and uninterruptedly into each other. All obstructions have been removed, all friction is smoothed out by the designer, there are no perceivable hoops to jump through.