They come into situations with preconceived notions and ideas about what they expect. Psychologists call these preconceived ideas schemas. People have schemas about every thing in the world. People have schemas about situations. People have schemas about other people.
People even have schemas about themselves.
And of course, anybody who surfs the web a lot undoubtedly has a schema about how websites are set up. With regard to websites, people are likely to have schemas about both content and about form. Memory research shows that if you violate people's expectations about content, you cause them to think. If you cause them to think they are more likely to remember the content. Plus they find the whole experience more interesting and enjoyable.