Well, the title probably says it all but nevertheless I am going to emphasize on this very essential web design tip.
A website would not gain constant stream of visitors or even repeated ones if users find the design inaccessible. A dumb and probably even useless fact some of you might say but people still forget it. You have to agree that the visitor is the most important person when drafting out a design. If you can successfully draft out a design thats appealing yet easily accessible to the visitor, then I assure you that your client would feel the same. (with the exception of 0.0001% :p)