Deceivingly Strong Information Scent Costs Sales (Jakob Nielsen's Alertbox):
If information scent is sufficiently pungent, people are generally convinced that they're looking in the right place. If that place doesn't contain what they want, they're likely to conclude that the site doesn't offer it at all.
Ironically, this article's title doesn't really say what it's about; since it's too technical/buzzwordy. Basically this explains why people leave your site when their categorisation of a topic doesn't match yours. That said; I'm still amazed when people can't find the search page on our site. It's linked from the word "Search" on every single page we have.