What is the difference between a dictator-like Emperor and one who protects and nurtures? The first follows the letter of the law (obeying the literal interpretation) while the other follows the spirit of the law (acts in accordance with the intention of the law and its spiritual principles). It's like the biblical explanation of a sheep being in a ditch on the Sabbath; a good person would work to get the sheep out (even though legally it is a day of rest) because it's the right and kind thing to do. The Wagtail card illuminates how an Emperor can keep from getting caught up in his own importance. Motacilla sp. has a habit of bobbing its tail, much like a happy child bounces on his or her toes. It thus represents being able to see joy and grace in any circumstance, instead of falling into the rigidity of seeing everything as good or bad.
The quality of mercy is not strained.
It droppeth as the gentle rain from heaven
Upon the place beneath. It is twice blest:
It blesseth him that gives and him that takes.
~ William Shakespeare, from "The Merchant of Venice"