One of the key challenges is being able to balance multiple inputs. There's obviously the team's experience and intuition which you can't discount, it's definitely an element, but you can't operate exclusively on that.
You also need to do sound research, and rely on your strategy and research teams to do their due diligence and legwork to make sure that they're validating some of the information, or ideas that the clients have had.
Also looking at metrics, and having a culture of experimentation is absolutely critical to not only come up with something that works, but to de-risk the investments that clients are making, in making a bigger creative campaign.
You're actually being very strategic about what's in play, and if something's being changed, how is it being changed across all channels? Are you maintaining that consistency so you don't lose people along the way?