It’s not a good idea to design a site so that only your target audience can use it. If you design a site for accountants using terminology that you think all accountants will understand, what you’ll probably discover is that a small but not insignificant number of accountants won’t know what you’re talking about.
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.