Derren Brown is a mentalist. His book about the trade is quite a spell binding (boom tish!) read.
Among the many gems, he discusses the fact that it is easier for him to play his tricks on those who watch him the closest. He flipped the old saying "for every action there is an equal reaction" by stating that for every bit of concentration in one part of the brain and on one part of his act, there is a loss of concentration in another part of the brain and on another part of his act.
This simple insight allows him to play with people. With great ease.
However, the people he as a magician fears most are the once who don't give him their full attention, those who glimpse out of the corner of their eyes to see what it is he is doing. No pressure is there on them to follow. They are not paying attention to a single part, but just glance to see the entire act. And then spot the cheat quite easy.
Sometimes we as admen to can get so deep into research/work or as a brand in our products, that we just see parts and are being played without even knowing it.
So remember to cultivate blank slates. Be it in your agency, or those that don't fit into the target group you do focusgroups with.
Those with no pressure to come up with anything, that have no stake in your brand. Have them glance your work, brand or thinking. Forget territorial pissing and be suprised to learn a lot.
P.S. over on his blog Northern makes an very good case for blank slates in your own life. Go and read.