I very often bemoan the fact that too many (maybe most) creative decisions are too influenced by styles and aesthetics the agency finds appealing. Or, just as unproductive, styles the client (and by "client" I'm talking about an individual, or committee -- not a corporation) finds appealing. But the ones that work are universally about the audience.
Now, I'm not suggesting focus groups make better creative directors than creative directors. They don't, clearly. But knowledge of, and enthusiasm for, the audience (an audience that changes with every execution) can help make a good creative director better -- and help turn a simple idea into a powerful story.