Consistency is one of the most powerful usability principles: when things always behave the same, users don't have to worry about what will happen. Instead, they know what will happen based on earlier experience.
Jakob NielsenOn average, when you ask someone to perform a task on a site, they cannot do it. It's not their fault; it's the designer's fault.
Jakob NielsenPopularity is the product of two factors: (a) how compelling material you offer, and (b) how easy it is to access it. Host free pirated movies and users will flock to the site, even if it's difficult to use.
Jakob NielsenThroughout this book, we've been evangelizing simplicity, but ironically, the practice of simplicity is not simple. It is easy to build a bulky design by adding layer upon layer of navigation and features; it's much more difficult to create simple, graceful designs. Paring designs to essential elements while maintaining elegance and functionality requires courage and discipline.
Jakob Nielsen