Don't make me think!
Or why "not having to think" is sooo important for you, me and by the way for your site.
Your web presence is all about the end-user and the user experience. But don't make your site fancy for the sake of having a lot of whoosh and bling bling. The user doesn't want to RTFM(*) so your web application or site has to be crystal clear. The user needs to find what he can do, what he wants, and what he's interested in without thinking. 
I follow this way of thinking as close as possible. Approaching the user in this manner finds its roots in industrial design and ergonomics. This is a perfect example of how industrial design and web design have a common ground. 
I didn't invent the term "Don't Make Me Think". It comes from the wonderful book "Don't Make Me Think: A Common Sense Approach to Web Usability" by Steve Krug. This basically says everything that a good design has to be. I truly recommend this book. 
(* RTFM = Read The F***'n Manual)