The majority of computer users are familiar with the Windows graphical user interface (GUI). Most people know how buttons, toolbars, and tabs work, based on their experience
with Microsoft Word or their email client. But contrast the consistent interfaces of client applications with online applications, and you find nearly every site does it differently. A user needs to learn how to use each Web application
from scratch. While many applications aren't particularly
complicated, it can still be a frustrating experience for a user to always feel like a newbie, needing to relearn an app
interface again and again.