When I began in this business, it quickly became clear that there are fundamental rules in graphic design. Things like, certain fonts should never be combined, don't use too many fonts, conservative businesses use conservative colours, make good use of white space, and certain colours NEVER go together...
Well, just as quickly it became clear that the way your business gets attention is by sometimes breaking those rules. Who would have thought that a bank, the epitome of conservative business, could successfully use lots of bright orange combined with royal blue - that combination is no-no - as its corporate colours! (I'm sure you know who I mean.) They broke the rules to show that they are an unconventional bank and are now reaping the benefits.
Or what about the Canadian grocery chain that created a North American marketing phenomenon with their advertising supplement which crammed way too much into a comic book-style booklet to promote their new products from an "Insider's" perspective? That campaign has been flourishing for more than 10 years.