Jakob Nielsen - Mental Models

Users don't just confuse search fields; many less-techy users don't understand the differences between many other common features:
  • Operating-system windows vs. browser windows
  • A window vs. an application,
  • Icons vs. applications,
  • Browser commands vs. native commands in a Web-based app
  • Local vs. remote info
  • Different passwords and log-in options (users often log in to other websites as if they were logging in to their email)

It's amazing how one misconception can thwart users throughout an entire session and cause them to systematically misinterpret everything that happens on the site. Through failure after failure, they never question their basic assumptions. This is yet another argument for complying with preexisting user expectations whenever possible. If you don't, then make certain that you're clearly explaining what you're doing — while also realizing that you face the added challenge of users' reluctance to read very much.