Consider that there is no sense of scale. The practical result is that it’s very hard to know whether you’ve seen everything of interest in a site, which means it’s hard to know when to stop looking. Even the people who manage Web sites often have very little idea how big their sites really are.
Don’t make me think
Being an expert in online usability Krug gathered his experience in a wonderful book. This summary of key thoughts will help you to remember most important principles and laws.