We'll tell you. It's this video of Duffy's Diet Coke ad — an ad so bad that it's made the singer a music industry laughing stock — being analysed and picked apart by a procession of directors, 'creatives', strategists and Duffy herself.
It's almost inexcusably horrific and is, of course, amazing and hilarious for that very reason — they could chuck on a laughter track and submit it to Comic Relief for this Friday's live show.
Never mind the fact that the whole thing revolves around a pop personality so dull that she makes Rachel Stevens sound like Courtney Love — our favourite bit is Duffy saying, with reference to Diet Coke's 'brand values', that "it's improtant to be selective about things that you want to do … it's about encouraging women to take control and say 'no'".
It's odd, isn't it, Duffy, because most female musicians — empowered or otherwise — would indeed have said 'no' to appearing in this toe-curling marketing circle-jerk.