How do you respond to the energy characteristics of a client?

I find that part of being a good consultant is understanding my client’s energy characteristics and how they deal with stressors, novelty, and conflict. I wonder though is it my job to be a cheerleader? Should I always play the same role in the partnership, carrying positive emotional energy?
Most great partnerships are fluid around emotional energy. Some have a yin and yang quality, opposite energy that is fluid and dynamic. Think Penn and Teller or Lucy and Ethel. What do you do to acknowledge the emotional characteristics of your client? Do you have ways to harness this energy to move forward?