Rules?
Yes,, all the time. Remember years ago when Land's End pioneered the customizable on-line model? My friend entered my measurements wrong--way too much bust and not near enough shoulder width. Everything I put on that model looked horribly frumpy and not at all like me. When I corrected the measurements, all of a sudden she looked slim and chic (despite my accurate tummy measurements) and the clothes hung on her like on a catwalk model.
That was when I realized that my shoulders are my asset, not something to be played down to make me approximate some "ideal" shape, hourglassy or whatever. As we are learning from the YLF sisterhood, we should embrace what makes us different and play it up, not down, for maximum flattery.
And my horizontally striped mariniere tops are my favourites now.