We all look for consistency in the world around us. Whenever you open a reference book, you expect the table of contents to be in the front and the index at the back. You have learned from reading books over the years that this is the pattern that books follow.
If you were to open a book and find the table of contents in the middle and the index at the front, you would be confused. You wouldn’t know how to navigate this book because the design breaks the rules that you have learned.
The same process works on the Web. Your visitors have learned certain rules about navigating websites, and while it might be tempting to design a cutting-edge site that breaks all the rules, that kind of design could cost you visitors.