In principle, the center of a circle is equidistant from all points on its perimeter. We need to know the edges in order to know the center. To know what is centrally acceptable to a group of decision-makers, it helps to know what lies beyond the outer limits of acceptability: what is unacceptable.
Practical Tip: Share wild ideas. Make bold proposals. Be provocative. Know that the group is actually well served when someone responds, “Now that is going too far,” or “That is stepping over the line.” Like a flashlight on a dark basketball court, shine it all over to find the boundaries.
If you are having a hard time defining how something should be, work for a while on defining how it should not be. Try stuff on so you know what does not fit. Explore side roads so you know which ones dead end. Work inward from what you know is out of bounds.
P.S. Do not become attached to clothes that don't fit or roads that lead nowhere.