Usability testing guru Jakob Nielsen explains how important our previous experience of the web is to determining how we interact with sites in his latest Alertbox article, Mental models.
From the perspective of a long time observer, he writes about user behaviour:
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…
He goes on to say…
When you see people make mistakes on your site, the reason is often because they’ve formed an erroneous mental model. Although you might be unable to change the UI at that point, you can teach users a more accurate mental model at an earlier stage of the user experience. Or, you might have to acknowledge that users won’t understand certain distinctions and then stop making those distinctions.