The more you watch users carefully and listen to them articulate their intentions, motivations, and thought processes, the more you realize that their individual reactions to Web pages are based on so many variables that attempts to describe users in terms of one-dimensional likes and dislikes are futile and counter-productive. Good design, on the other hand, takes this complexity into account.
Faced with the prospect of following a convention, there’s a great temptation for designers to try reinventing the wheel instead, largely because they feel (not incorrectly) that they’ve been hired to do something new and different, not the same old thing. Not to mention the fact that praise from peers, awards, and high-profile job offers are rarely based on criteria like “best use of conventions.”